It does sag a little bit, but not worryingly so. As I mentioned, it often rests on top of the large plastic boxes I place underneath, and I put in a small wooden brace at the entrance. You could definitely build it slightly smaller, or put in a more substantive center brace — like a sheet of plywood that fits into the groove of the bed liner and is the exact height you want.
A dust mask or respirator will protect you while you're working, but won't do anything to protect you or your family from suspended particles still in the air. For this reason, an air filter is an absolute must if you work with woods indoors (I know of guys who sneezed out sawdust after working too long without an air cleaner). It's possible to make your own air cleaner out of box fans and furnace filters, but retail air cleaners will usually be much more compact. If you go that route, we recommend Wen 3410 3-Speed Remote-Controlled Air Filtration System for smaller shops.
Every aspect of your store should flow from a clear statement of who you are and what you stand for as a business. From the sign hanging proudly outside your store window, to the color of the wallpaper in the in-store restroom, every detail should contribute to conveying your unique purpose and brand to the world. This consistency should also be applied to all your online assets, for example, your website design.
Another option to consider is an expensive but efficient Festool dust extractor. These dust extractors are designed to work with other Festool tools, but they also match up with most other brands' compact power tools as well. A nice thing about Festool's vacs is that the hoses dock neatly inside the units. There's almost nothing I value more for a compact shop than self-contained storage.
In an indoor or basement shop with industrial carpeting, lay down inexpensive laminate flooring to make your life a bit easier at the end of the day. Be sure to anchor the panels or place a large rubber mat beneath to keep them from sliding over the carpet. (Covering up your carpet is even more critical if you want to go beyond wood and work with a material such as aluminum in your indoor shop; metal shavings dig into any kind of carpeting and are incredibly frustrating to clean up.)
I'm in the same boat. In Florida, we don't have basements, so my dedicated portion of the garage is 10' x 12'. In that space I have very neatly packed: 8' bench, Cabinet saw with 50" fence, 18" bandsaw, Dust collector, Joint, Planer, Drill press, Compound miter saw and a medium-sized hanging tool cabinet that holds all my nielsen stuff. I find myself moving my stool several times an hour just to work... Can't wait to move into a new house some day!