Hi Tony
Welcome to the forums
Heaters: Yep go with two 300w Not much price difference from 200w
Substrate: Since you don't have an Under gravel filter your are NOT limited to what you use.
Plants: Use artificial plants if you plan on getting lots of fish that like to eat plants, as this will make your tank look as if it was planted... not a barren dessert :lol:
Otherwise go for live plants... don't have to worry about wiping the leaves clean from algae.
Fish... really depends on what you want, but definitely go for some Bristlenose cats to keep the algae down. But as Pearlyred said add fish a couple at a time so that you don't throw the bacterial balance of the tank out of kilter.
Also as others have said you are missing the other tanks.... once this disease of MTS hits you, there is no cure
Happy fish keeping and if you got any more questions post them up here in the forums and somebody will definietly help you.
Wok