all your questions are easily answered by opinion....
First, should you choose to stack your LR against the back wall, you may develop scratches in an acrylic tank. glass tanks do not scratch this easy. also, make sure there is not an absurd point of pressure on any given pane of glass in your tank. the glass CAN and WILL shatter. when stacking LR its important to place it on a sand bed or some eggcrate, or even a peice of cutting board or plastic to distribute the weight of the LR so it will not shatter any pane of glass, also be sure to not allow for "toppling" of LR. a falling peice of rock can result in broken glass... snails and some crustaceans, as well as some fish are to thank for this. epoxy or crazy glue work for placement of frags, but do not soley rely on this to keep the rock from being moved, as the bonds, if improperly done, will not last long. Doni (woodstock) uses a clay-type stuff that will cure underwater, you may want to try it, as it may be stronger than crazy glue. (IMO) placement helps when you determine how easy it will be to clean the tank in corners, the back pane, or getting absurd amounts of snail poop along the back wall of the tank. LOL. this does come in handy to remove as soon as possible.
Second, "nano" LR is only regular LR that is broken, or "cut" to fit in our small worlds of wonder. you can do this too with a concrete floor (clean) and some elbow grease. to break LR the way you want it to be broken, simply chisel the area you dont want off, or if you want a random peice to be formed, throw it against the floor.... (not your spouse)
... the rubble helps also, as you can use it to "grow out" frags, shrooms, zoos, or place it in your filter for excellent denitrification properties. basically, get the LR YOU like. your not setting up a nano for anyone else, and if you like LR with small pores, get it. if you want it shaped a certain way, do it!!! LR is not "alive" and the only thing youll hurt is a hitchhiker maybe, or yourself if you throw the LR on your foot instead of the floor (happened to me, it hurts, trust me.
) when you order LR, get the LR you think will look best to you in your tank, whether its Tonga, Venutian, Fijian, or others, or even combinations!!!. since the LR will be shipped, you can easily epoxy peices together, form canyons, etc. before you place it in the tank, or after if it is going to be a big peice. a regular two-part epoxy that is safe for marine life should be used, and one last thing:
no matter what you do, have fun!!! youll love this hobby, and expect some great things to happen!!!