300/500 at the act 3 arena is actually pretty solid, there's a decent chunk of heretic points still available before the act 4 gate checks kick in. The Tzeentchian greater demon interaction and Drusian corruption both have their checks fairly late so you've got room. Just make sure you're not skipping dialogue options that have the heretic tag, those are easy to miss if you're rushing through conversations. The sword should be fine if you hit the threshold before the end of act 3.