If I add lower control arms and not upper, should I reinforce the floor?

Not sure that you need it, unless your car takes abuse weekly. Although it is always better to prevent somthing from happening, then not, and have to spend more time, energy, and money fixing it then you would of if you prevented it in the first place.

wild rides sells a few setups that are good. the reinforcements for the upper and lower control arm are mounts are pretty beefy and seem to work pretty well from what i understand. i know a few people that had problems with their mounts and put these kits in and the problems dissapeared. they are weld in or bolt in.

WILD RIDES

If you don't want to the buy the kit, i hear that you can just finish the welds up a lil better. But i suggest if you are going to do anything to prevent anything these kits would be best.
 
Don't need it unless you plan to go straight to running slicks and launching hard all the time. I use the Lakewood LCA that change the mounting position for better traction. Running FRPP UCAs. After a summer of drag racing and daily driving I still don't have any signs of damage to the torque boxes.
 
You could weld up the torque boxes if you have the know how...just dont set your backseat on fire! I launched hard (1.6 60fts) probably 300 times with just lower's and there was no damage to the torque boxes...last time I was in there I welded them up for peace of mind though.