I suggest that you employ a good interior designer. Ask all your friends, neighbors, friends of friends, for references. You need someone with experience and yet reasonably priced, someone with common sense. Best of luck.

I suggest you think transitional/ multifunctional rooms. You want what works now for your family, what will work when your kids are teens, and then when they are gone. Your idea about the play room now, exercise room later is solid. Also I would consider an office/guest room that can be used either or depending on the need of the day. The storage idea is right on, and absolutely put a bathroom on that level. This is an expensive endeavor you want it to work for you over the long haul the same way the rest of your home works for you.

Take a look at Candice Olson's website. She has done some awesome basements.

I agree about Candice Olson. I think her secret, frankly, is that her lighting is outstanding.

I also think that a bedroom and full bath, and family room type of hang out area is the most useful to the widest number of buyers. And of course the storage.

From a young college student living at home to save for a house, to an inlaw, to an overnight guest. This is a very useful thing. If your home has outdoor access (a walk out basement), then I would very strongly recommend making the bathroom space fully ADA handicap sized so that an older parent could live there (wider door, grab bar style towel bars, not much extra expense, just more planning).

I think a sink, small fridge with freezer, and microwave are adequate, and that doing more would not be a good investment if you are moving soon.

We have five rooms in our finished basement...laundry room, library/office, work/junk room, family room and bedroom with full bath. It was great while the kids were growing up, and it has been fabulous as as guest suite now that they are grown.

One thing I would advise is to tile the floors and use rugs. Don't carpet. Basements don't leak...until they do. My house was forty years old before the basement leaked, but my son's new construction was only two years old when it did. They didn't even realize it until the mold and stink set in because of course, the carpet absorbed the water. It is truly amazing how much water carpeting can hold! We have ceramic tile and room size rugs. His carpeting had to be torn up and replaced. Also, sewers occasionally back up. With ceramic tile, you just have to hose and squeegee.

Have fun with this. It will pay off for years, and it makes your house so much bigger.

I meant to address your full bar question. My son with the formerly leaking basement has a bar like you describe. Beautiful to look at, but alas, not very useful. They entertain often but rarely downstairs. Even tho they have everything down there including a dishwasher, the parties stay upstairs. People tend to run up and down for a while, then they start bringing up the bar goods and hanging out upstairs. DIL has tried everything she can think of to prevent it, but it happens.

Their basement is English style with 10 foot ceilings, bright, beautiful, comfortable. They do use it now for parties for their two little kids, 5 and 8, but anticipate having to do something with the booze when the kids get older.

As mentioned by a previous poster, lighting in a basement is a major consideration. The description sounds like yours is a conventional space, all below grade so natural light is lacking. Plan for plenty of cannister lights and add wall sconces, pendants and table lamps. Use dimmers whenever possible.

Take a stab at a rough design yourself. Using graph paper, draw the entire space to scale. Indicate location of fixed objects like your furnace, plumbing, stairs and any support posts. When we designed ours, we placed masking tape on the floor to better imagine the build-out and used this to place lighting.

Is one of the windows an escapement window? You'll need one in order to have a bedroom. Provide for a dehumidifier and have a return air for your HVAC. Auxulary heat might be necessary for the spring/fall seasons when the house system is not operating often.

Our basement is primarily for entertaining so more of a great room concept. We do have a full kitchen, TV area and storage incorporated into approximately 1,000 sq. ft. overall, with maybe 800 finished. Photos are linked, including our plan, with descriptions below many pictures. Everything DIY. Hope this helps and good luck with the build.

Here is a link that might be useful: Our Basement

Storage, storage, and more storage.
Think about how you want to use the space, and plan plenty of closets to accommodate all the things required. Otherwise, you will have a job on your hands to keep it from getting junky.

So here is more than you wanted to know about what we did:

When we did our basement, which also included a long one-car garage along half of one side, we put in a u-shaped light shop space (no power tools except drills and the like) at the end with a deep sink in the center of the U, one side dedicated to plant care and flower arranging, peg board (painted white) lining the walls up to 6'8", and a deep shelf on ordinary white hardware store brackets above that.

I recycled two L-shaped wooden countertops that were cast-offs from another project, stained them, and finished them with spar varnish.
I designed the supporting structure (painted dark gray) to accommodate three mobile storage basket units that I already had.
I painted the wall over the sink (no pegboard there) with chalkboard paint, which was great for jotting down measurements and things to go on the shopping list.
We used plain old rectangular florescent tube fixtures in the ceiling, which gave exactly the kind of clean light we needed, and a couple of boxes of peel and stick vinyl tiles on the concrete floor.

The short wall of the house which had the garage door and the entry door from the driveway was our foul-weather entrance, and had a fireplace in it, so I allocated half that space to a warm sitting area, and put a trestle table to serve as a desk behind the small sofa that faced the fireplace. I dealt with the high little windows along the long wall (with a lovely view of the bottoms of the boxwoods along the front of the house) like this:

Behind that area, I created a hallway to the back space by building a cedar closet on one side, which ran under the staircase, and a long deep closet with three doors in the wall and deep shelves lining the whole thing on the other. Where the cedar closet ended, under the low part of the stairs, I built in a niche for a long 2-drawer lateral file cabinet.

We had the stairs rebuilt to create a 3 x 3 landing at the 3rd stair up, so we could turn the bottom stairs to face into that hall, and create an easier and more attractive entry to upstairs. Beyond that hallway was enough space for a pantry closet and a wine closet along the short wall, and a chest of drawers perpendicular to that. Beyond the stairway was the door to a new laundry room and a walled-off area for the HVAC and hot water tank (with louvered doors), and between the laundry room and the back wall of the garage workspace, we put in a big bathroom with changing space for anyone using the pool, or coming in from the garden all covered with muck.

We did the bathroom very economically - the things we spent any money on were a Venetian marble shower stall and long countertop with an integral sink.
Instead of a vanity, we mirrored the wall and attached a simple framework with a stained birch plywood fascia along the wall to support the countertop, built a 10" high plinth along the floor under it, and put big baskets of towels and washing and sun supplies on it.
Then we ran a 2x10 along the wall opposite the shower with many hooks for damp towels and bathing suits, and added a simple garden bench.

I loved it. It made my too-big house completely manageable.