hey, your questions are good, no need to feel bad about them, at least you are learning instead of rushing into things. also someone may have the same questions as you, and come across this thread.
no, you dont need a "filter" such as a HOB or a canister, but i liked having a HOB on my old 10 gallon tank. when i first added the sand, it was very cloudy, so it helped to put the filter pad in there to catch some of the dust. i removed it the next day. also, it helps with surface agitation. a couple months after the tank was set up, my HOB mysterioiusly kicked the bucket. i thought, oh well... no biggy. i was wrong. i soon developed a protien film over the top of the water. i didnt realise that i needed one all along. untill i got a new one, i had to point my 2 most powerful powerheads at the surface to create the movement i needed. also, i think my fish was suffering from oxygen deprivation before i did this.
10 to 15 lbs of LR sounds good to me, and no, you dont need a filter.
2 X 200 powerheads will be fine.
i think it would be fine to get a 200 GPH and a 300GPH powerhead. this turns your water over about 50 times. i think it would be fine to have one powerhead stronger than the other.
if the water is cloudy, i would be fast to blame it on the sand, so adding more wont really help. adding more LR also wont help. about all you can do is wait for it to settle, add a sponge to your powerhead, or add a filter. if you go with a sponge or filter, i suggest removing the filter pad from the filter, or removing the filter completely, and removing the sponge from the powerhead.