If stick built the one running perpendicular to the long wall is likely a load bearing wall.You can get an experienced GC to look at it and they will be able to tell you.If it is load bearing you will need an engineer to draw it up so you can turn it into the city.Not that expensive.

Do apartments, but have a couple of clients that own strip malls.First, any type of property can get overbuilt, however, both guys are happy because:1) High traffic count and street egress and parking (kinda tough getting all of that in one place)2) Site exposure - You want ALL the storefronts facing the street and NOT a mall that is perpendicular (ie the short end) facing the street3) Get a good anchor (like major cell phone guys) that bring a lot of traffic to the mini-mart since they're there already4) Try to avoid some businesses like small specialty groceries by first-timers that stop paying rent after 3 months since they have no clue on how to run a store.

The floor is comprised of 2-layers of 1/2" XPS hardboard insulation laid perpendicular to each other with particular attention given to ensure seams did not overlap.

The joists are then hung from this perimeter by inserting them perpendicular between the outside perimeter and the field laminated 4x12 ((2, 2x12s lag bolted together)intermediary cross beams that are pinned to #4 rebar that I cast into smaller, interior support piers.

If you have a hardwood floor it could be the floor itself or the subfloor and hardwood floor rubbing against each other due to a breakdown or missing underlayment.If you have a sleeper flooring system you will have 2x2-4 sandwiched between two layers of subflooring and should be running 12" on center.If you do decide to do the drywall method here is a link to resilient channel http://www.soundproofingcompany.com/soundproofing1...If you do decide to use this make sure that when you hang the drywall that the screws are not too long so that they don't go beyond the channel into the joist or other wise you will defeat your purpose. also when installing the channel you should install it perpendicular to the joist and don't forget to box around any fixture with the channeling so you can properly attach the drywall to it.

This is what I see.... the outside joists (the joists perpendicular to the exterior wall) are supporting the entire load of the deck.

Then, put "screeds" in perpendicular to how you want to run the flooring.

The problem would then be the lack of a full bath.My other thought would be moving the plumbing and putting a tub perpendicular to the existing location.  

It runs perpendicular to the ceiling joists.Ceiling joists run from outside wall to outside wall. 

The trick to keeping the paint off the ceilings without a spray guard is simply to keep the sprayer head pointed perpendicular to the wall, not to tilt it up.