Hey, good for you for upgrading your betta! I have over a dozen bettas and they make the greatest pets..like little water puppies!
And welcome to AA
I would get a heater with a dial and not a preset temp, otherwise they typically won't get warm enough. Bettas do best at 80F. He may be fine with the filter flow..personally in 5's and 10's I always baffle the filter for males. Here's how:
Filter Currents: A Betta's Worst Nightmare
Bettas are very prone to things like constipation, bloating, and swim bladder diseas, so diet is important. I feed a high quality small pellet such as Hikari or New Life Spectrum 3-4 days a week, and thawed frozen food such as bloodworms or brine shrimp 2-3 days a week. 1 day per week feed only a few pellet sized peices of blanched shelled pea. This will help clear them out and prevent these common issues. Avoid freeze dried foods. Their fins are incredibly sensitive. Everything that will go in their tank needs to be checked over thoroughly. The pantyhose test is one method..run pantyhose over everything going in the tank and if it snags the pantyhose, it will snag the betta. I use a metal nailfile to smooth out any sharp edges or points on decor, and generally stick with live and silk plants. A couple of my male bettas lay on the ground so I typically use a nice smooth substrate in their tanks as well.
A side note, I do not recommend betta sororites. I just split up my sorority of 6 females. After keeping so many bettas solo and in community tanks, I could tell these girls just weren't happy. They were surviving, but not thriving in the same fashion.
Also to clarify, you'll want to gravel vac always when you do your weekly pwc