Definitely folding tables for your gaming. I have a smaller space of about 12' x 9', but it's wargames only, no study. I can put up a max of 8' x 6' and still leave room around it for players and storage.
Ikea is your friend for storage. A mate of mine has a LOT of their glass fronted wall mounted display cabinets to house his collections.They come with frames surrounding the glass doors in various wood finishes and are not too deep. Just right in fact. Much thinner than a bookshelf. Lighting and glass shelves inside.
I personally went for the Ikea "Besta" units. You can configure a mixture of glass and solid doors, the latter with lighting and display shelves. It's a full depth run of cupboards which holds a lot, and can display models or armies in the cabinets. Paints and terrain etc get a solid door.
P interest helped me a lot when I was designing my room. Search on that site for wargames room and wargames table and nick all the best ides.
Oh, yeah, and don't forget lighting. I have a seperate ceiling mounted circuit with several ceiling points each fitted with power saving light bulbs which throw out iirc 100w (equivalent) light power.
Folding chairs take up no space when stowed, and I do have a 4' x 2' baize covered table which is permanently out. As well as being there for board games, it exactly matches the height of my fold away bigger tables to extend the surface. Mainly though it holds troops waiting to arrive.
I put a 4x 2 piece of hardboard on top and attach my daylight lamp with magnifier and I have a painting station where I can leave stuff set out to try to do 1 hour or so every day…..
I am a subscribing member, do if you drop me your email address I will send you some photos.