I'm sorry to hear about your Betta buddy. They have so much personality for a small fish. Your new one is nice though!
I have one at work in a 3 gallon, planted, and one at home in a 5 gallon, planted. They get fed once per day, skipped days here and there. Maybe 5 pellets at a time.
I do 50% water changes 1x/week in all of my tanks from 3 gallon to 65 gallon and it works well. 90% 2x/week I would think could be stressful. Check your water parameters - if ammonia and nitrites are 0, and nitrates are under 10-20, you don't need to do as many changes.
You could add a sponge to the intake to help keep his fins from getting caught in it, and it might slow the flow a little. You can also cut up sponge and put it over the output and that can help slow the flow. People also make baffles which you can google. For me, I've done OK with using sponges.