Summer, what is your style and budget? For instance, itemize for me what you would like to spend on each., tub, vanity,tile ect. And are you modern or traditional? I can come up with a really nice bathroom on a budget that won't look like a HD bathroom.

You have a wonderful space, with lots of possibilities. It's difficult to design a bath without knowing the budget, but here what I would do if it were my bath.

*Install a 72" vanity, with two (2) 30" sink cabs, and a 12" stack of drawers in the center. Make the bottom drawer a min of 9" deep, if you need larger drawers take a few inches off the sink cab. Check with local custom cabinet makers for price. Most of them are slow right now, and you'd be surprised at the cost. Doesn't hurt to ask.
*Install two (2) undermount sinks (19x 15 ish).
*Remove/ replace brass towel bars (especially the one over the toilet).
*Pony wall- You could leave it and move the electric outlets from under the mirror to the sides of the vanity (much safer). Or remove it all together.
*Mirrors- I would install recessed medicine cabinets at each sink.
*Shower- add plumbing for shower, tile walls and floor. If the budget allows install stone, or full bodied porcelain tiles. Go with neutrals and add the color in your art/ accents/ towels. Brown and blue are beautiful, but you'll want to change eventually.
*Tile- larger tiles on the floor will make the room feel larger. 18x18 on the diagonal. Shower wall- there are thousands of designs- all depends on your style.
* shower curtain vs glass door- go with the curtain, but keep it open. If over time you don't like it you can replace with glass. I'm with you- kids will never keep clear glass clean!

Good luck! I can't wait to see pictures once you're done.

We honestly haven't even thought about a budget, but I'm guessing $3000-4000. We probably won't have to pay labor on anything, as my dh has already remodeled our other 2 bathrooms himself. And, honestly, I'm pretty ok w/ it looking like Lowes or Home Depot because I don't want to over-do the bathroom above the rest of my house. (Does that make sense?)

As far as my style, I have the rest of my house decorated in country/americana/shabby chic. BUT when we remodel the bathroom, I want it to be neutral/marketable because I think we will be selling this house w/in the next 10 years.

If you want timeless, then do white for your fixtures and tile and forgo the blue and brown except in the paint and accessories. Maybe do the vanity in the chocolate, but with a white vanity top and sink. 4K isn't a lot to spend on a bath, even if you are DIY on the labor. The vanities will cost you around $1500-$2500 if you do the more custom double vanity with the drawer base in the middle, and that imprisons you to a more expensive custom counter as well. You just went over budget, and you've only got as far as the vanities. Despite the expense of redoing the plumbing, I think you can stretch the budget further by having 24" individual vanities that you can find as stock at one of the box stores and individual mirrors above them. You can probably do that for $1000, including the tops.

FOr the tub, to be able to use it as a shower, it needs to have an integral tile flange on it to seal out moisture infiltration from behind your walls. You'll need to tear out the current tile to ascertain if it has that. If it doesn't then replacing it with a nice, slightly deeper soaking tub can be done for around $400. If you want a jetted tub, American Standard sells a $699 one at HD with a lifetime warranty and the new system that angles the internal jets downward so that all the water drains out when you empty the tub. That keeps it from sitting there getting yucky. It's a great buy, and can be used as a shower too. The real necessary expense is updating the tub faucet with a tub/shower valve that contains the new anti scald technology. A thermostatic valve is the better but more expensive choice here.

Classic subway tile mixed with some classic 4x4 and 6x6 for the shower walls would let you do an interesting tone on tone pattern but not break the bank. White tile for the floor may seem "boring" but it lets you use any color accessories that you want to liven it up. And, using the layout to add pizazz just like the shower will work to add interest also. Paint the walls a pretty silvery blue and put in chocolate and blue towels and your vision is complete--and on budget!

PS. I'd also replace the toilet with one of the newer technology low flow ones. Lowes sells a Jacuzzi brand one in stock that is fully skirted and will be a lot easier to clean than all of those nooks and crannies where the P-trap is visible in the regular models. I think it's around $225 for that.