I started the aquarium hobby with FW tanks. I've worked with FW for about 3+ years before I ventured into SW over a year ago. I still have over 15 fw tanks of various sizes...planted communities mostly.
You don't need to worry about the PH in a freshwater tank.....unless it's insanely off one way or the other. As far as the fish are concerned anyway. You have more to keep an eye on with planted tanks, but with what you're planning to do...no worries. Freshwater fish will acclimate to whatever PH you have, just take your time introducing them to the tank, they should be fine.
You don't need a substrate in your tank and a good sponge filter will take care of any bio media you'll need. Get one that's rated for the size tank you have. Personally I think sponge filters are the best things on the market for filtering a tank. They're super easy and cheap to maintain....no new filter media to buy, you just rinse off the sponge in your old water when you do a wc. Easy......
You do need to let the sponge run in the tank with an ammonia source and test the parameters to make sure it cycles properly. Ammonia, Nitrite and nitrate are the only testers you need when checking your cycle on a fw tank. You can use a cocktail shrimp as your ammonia source, just toss it in and let it cook....keeping an eye on the ammonia. When you measure a zero ammonia and get measurable Nitrites, your tank is cycling..........then you wait for the nitrites to go to zero and the ammonia should also read zero and you should be good. A small measureable amount of nitrates is ok up to 20 some say....after that you need to find out why, but with a bare bottom tank, that shouldn't be a problem at all.
Measure your PH to see what types of fish would be more suitable. High Ph/hard water is good for african type cichlids.....lower PH/soft water and the South American type fish do better. But either is fine, like I said....most FW fish are pretty adaptable no matter what the PH or hardness is as long as you acclimate them carefully.
Some decorations would be appreciated by your stock, but again...not entirely necessary. Breeder tanks have nothing but sponge filters and fry/juvies in them. But, you could purchase a few plastic/silk plant type decorations or fake caves .....wouldn't hurt.
40s a nice size....you'll have fun selecting what fish you want to keep...do some research though and find out what would be more suitable. I recommend at least getting a few cory cats....they do an excellent job of keeping the bottom of the tank nice and clean.
