Downsizing Enough to Fit in a Tiny House

Earlier in the year, I found myself thinking fairly often about what it would take for my girlfriend and I to downsize our "stuff" enough that we could comfortably live in a tiny house on wheels. I feel like I would love the freedom to buy property and move the house with us rather than having to try to sell a house and buy another if we should choose to relocate in the future.

We currently live in a 1,000+ square foot apartment with two bedrooms, a large living room, a walk-in storage closet, a small "den", a bathroom with a full size tub and a kitchen with two small closets. One of the bedrooms functions as a craft room and the den is used as a home office but both end up also being used for storage. I'm not going to lie, we have a lot of stuff. Some of this stuff hasn't even been unpacked from the move before last when it went into storage for two years.

So while we do have enough indoor space (and central A/C, which is nice in the summer) we also have horribly loud downstairs neighbors (the second set of them in two years) and we pay too much in rent, especially for the location and the lack of amenities. I have lived within two miles of where I grew up for all but 4 years of my life (2 college years a few hours North and 2 years an hour West) and I'm feeling more and more like it's time for a change of scenery and weather.

If we did decide to try out a tiny house on wheels, we'd need to weed out a lot of our stuff and try to figure out what it is we need to have then take that into consideration when planning of the layout of the space. In our current apartment, most of our time is spent in the living room, so I think that would be the primary space we'd need to plan around. We'd give some extra consideration to the kitchen layout to try to fit a full size oven and sink. I'd also attempt to make the living space flexible enough to occasionally do things other than just sitting around watching TV. Hopefully, having less indoor space (and maybe moving to an area with more mild winters) will help push us outdoors more, though. I miss being outdoors.

I'm thinking that we'd end up getting an additional storage shed for the larger outdoor items that we'd need/want (outdoor tools/bikes, etc.) that are currently in storage with family members but we have a lot of other stuff that would have to be eliminated in order to comfortably fit in a much smaller space. I know, for me at least, that many of the things I have accumulated over the years (mostly CD's, magazines, books, computer parts/equipment, snowboard, skateboard, guitars) could be weeded out a little more aggressively than I've done in the past, but I'm worried that there are things that we'll miss when they're gone. I'm sure a lot of that is just sentimentality (random things from my childhood, souvenirs), but there are things like my girlfriend's sewing machine and books and my desk and CD collection that take up space but we wouldn't really want to part with. Those are probably the biggest things that would be tricky to work into a tiny house floor plan. Then there are some other things that I'm conflicted about. I've always wanted to learn to play guitar and I have two guitars and an amplifier. However, I haven't touched them in the past 5 years except to move apartments twice. Will I make time and the effort to learn someday and wish I kept them? Honestly, probably not, but will I regret getting rid of them and end up buying them again?

I'm really not sure where to start, though, aside from just taking passes through the stuff and selling/donating/recycling/discarding the things that I know I can do without. Then we're left with the more tricky/sentimental things. I don't want to end up moving a bunch of stuff and putting it in storage, so how do you work through getting rid of that kind of stuff?