I really want it, but have already started playing and am not willing to reroll. Saw no mention of existing save games in the readme, so does anyone know if this will be ok with an existing save game? Shall I rebuild by bashed patch if so?

Yes you can add it without starting a new game. It is generally good practice to rebuild your bashed patch any time you add or remove a mod.

ok, cheers, I'll give it a shot.

I was just thinking, shall I run my list through BOSS with stirk included, or will changing my load order around mess up my save?

Running BOSS with stirk included is fine. Load order shouldn't hurt your save.