Hi and welcome. :)
I use the same exact filter in my tank. I had to use aquarium sponge to baffle the intake and the top lid to decrease the flow. I know most people only baffle the top, but I noticed the bottom part of the filter would suck up their fins if they got too close. Since Snowy is also a crown tail, I figured I would mention it. :)
I use a different heater but it has the same wattage as your's so you should be good. In fact, it makes the water a little warm at 79-80 degrees. I haven't had any problems but I use this thermometer
since I don't like the stick on type either. I can't have a finicky thermometer when my tank is the smallest size recomended for my heater. 50watts should be good for your 10 gallon, but don't go above 100watts or you could risk over heating the water.
Aquarium salt is only for emergencies like fin rot or an infection. If you use too much salt, you'll make salt water instead of fresh water. So you should use water conditioner to treat your water during water changes and save the salt for illnesses. I use NovAqua Plus
to condiction my water. I also know some of other members also use Prime
. Any conditioner will work well if it removes chlorines and heavy metals from the water.
What kind of decore are you going to purchase? Bettas like to explore, so I gave my fish as many silk plants as possible and two hiding places. You don't have to go overbored (like I did ^_^;) but Bettas do need at least 1 hiding place and some plants. My bettas like to chill in their hideouts, but some other bettas like to rest on plant leaves. It really depends on the fish.
When you do divide your 10 gallon tank, I would suggest either 1 or 2. If you divide it once each fish gets 5 gallons and 2 dividers would give each fish at least 3 gallons each. Once you break the tank up into 4 sections, each fish only gets 2 gallons which can be a bit of a bio-overload for your filter. I think most people will agree that 3 bettas in 10 gallons is a safe bet. :)
Well, thos are all the suggestions I can think of. I don't know if any of my ideas are epic, but they should be helpful. Good luck.