Small bands rehersal/studio room

The common theory behind bass traps is the more the better.

Now, you just have to remember that the more bass traps will ultimately deaden up the room but to offset the deadening is to add diffusors so never worry about adding to much bass traps.

Take note what the experts or most of us will say, you can't get enough of bass traps the above just gives you an idea of what will happen when you do add a lot of traps not saying not to add them. My apartment is small but I have covered nearly 50% with no diffusors and it is no where near close to dead.

So the answer to your question, do you need to add traps all the way down? Yes, if you want. You can go about this in two ways, firstly you can just add to any corner you can get to regardless of all the way down, when we say corners we mean all floor corners and ceiling corners wherever and anywhere. 

Or, you can just find out where your bass build up is and add traps there to start off with. Then add all the way down. The net will tell you, even Arqen's site says which corners are more prone to bass than others follow that path.

Diffusors usually go at the back of the room, so in a HiFi room its where the speakers point to, its the reflection from there that adds to the diffusion. In a studio I would say the diffusers will go around the instruments(probably behind) not where the window are well it depends where the windows are in relation to the instruments. Covering them is not a bad idea just depends on the windows location. What is the priority to covert them to stop the horrible sounding glass reflections or to add diffusion to the instruments?

www.youtube.com/watch?v=vb30CICG68c

Take note how Ethan plays his instruments into the diffusor, take this as a base to how to add diffusors to the area.