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.

I have a sewing/craft room set up, which I use almost every day. I can't find my camera cable right now, so I can't upload a photo, but I had a thought about your space. You really need a sewing machine space AND a table space because half of sewing is laying out the pattern, cutting, etc. I'm pretty sure I'm at my sewing table at least as much as I am at my machine itself. So, what might work really well for you is to get an old armoire from your local CL, and create something like the attached for the machine itself. Then you could position the table about a foot and a half out from the wall so that the person using it would stand between the wall and table, and could view tv. You could use the space under the table for wheeled carts which could hold storage supplies. Honestly the best storage I have in my craft room is the 8 foot long pegboard I put up. Everything hangs there: scissors, rotary cutters, rotary rulers, tape measures, etc. I can clean up in under two minutes, which helps me keep the area neat. The third element that is critical to the space is an ironing board. You could easily accomodate that by putting a fold-down board on the wall. They even have attractive cabinets for them now. Here is a link that might be useful: Sewing Cabinet from Armoire

I'm with those who've suggested creating a dual-purpose room. It sounds like you would use the crafting/project space, so why not set up half the room (or at least a corner) with a work space for yourself, and find some (gently used) fitness equipment your husband wants? Then you could see how you end up using the room before devoting more space than necessary to one purpose or the other. When I'm ready for another area to have to clean and maintain (which won't be for at least a couple of years), we'll finish our basement. We have the floor plan roughly worked out, and one room will be a combined fitness and project room. Right now the fitness stuff is set up in a corner of the unfinished basement and only sees use on the coldest mornings of the year, or occasionally when the kids are playing down there and it's too hot to run outside. I'm not sure it will get much more use even when finished as I'd much rather be outside moving around, but it's nice to have during periods of extreme weather. My sewing machine is now in a corner of our bedroom that's not ideal, but better than having it shut up somewhere. Projects end up all over the house, spread out in the living room or dining room. There's a kids craft table spackled and ready to be sanded sitting in the middle of the living room as I type. I know I would use a project space if I had a designated one, but the thought of having to clean (and decorate!) the basement when I'm still working on the main floors is too much for me at the moment.

3x6 meters is not a lot of space for what you want to do. You may be asking too much of the room. Music tends to spread out, and you need a bit of space to use it. Exercise equipment is less likely to be used if you have to wrangle it out of a corner, and then you have to have room to use it. Even small dumbbells. You might be better off keeping those under your bed in a roll-out box. (although, for me, out of sight is out of mind.) But if you really want them in the space, you might find a wall rack for them, and put it at the front of the space so you don't have to climb over the music stuff to get to it and use it. Hmm, I'm not sure I'd want small children playing in a room with expensive electronic and music equipment and dumbbells in it. Unless they are being supervised on the equipment. And with all that, two sofas might be too much. one, maybe. All that said, I'd put the music equipment at the far end of the room, with a divider of the bookcases or something. Keep the kids out, and your DH will appreciate the privacy. In the front half of the room, you really have room for only one sofa, and the tv will be small because you will be only 2 meters away from it.