For substrate I use sand since all the crap gathers on top, and since the tanks have high flow, it gathers in certain areas making it eaiser to remove. I have gravel in one of my tanks and its only as its planted, I would certinally favour sand, but if using gravel, make sure its smooth.
For the botia tank, canisters with either an internal or powerhead/s for flow. I have found that the Fluval + range of internal filters produce a good flow, plus you have spare space for additional sponge media. I have a couple of fluval 4+ internals on my 5ft until my circulation pumps arrive and they deliver a good flow for that length of tank.
For Powerheads, I have found Maxijets to be decent and quiet.
For the botia tank, you might want to consider some dithers (small barbs, small rainbows etc) to make your loaches feel that bit more sequere in their home.
Decor, I always keep mine as natural as possible, but long as you have plenty of hiding places spread out about the tank it doesn't really matter. Pipes are great-I have great success with these for a variety of species. You can make them more 'natural' looking by getting some java moss to attatch, or coating it in sand and gravel.
Plants-I don't know if your thinking of live or fake. I have found B.striata to be well behaved in my planted tank (bet I say this and I come down tomorrow to the entire tank in shreds


Ashleigh