Training an overexcited, bitey puppy

So I've read everywhere that puppies need to sleep 18-20 hours a day. So we're having 20 – 60 min play, feed and train in-between 2 ish hour naps with toilet breaks inbetween. The toileting (don't wanna jinx it) is going well. She's managing sit and understand when we've been for a wee, we get to sit and have a treat. She will also sit before dinner but this one is tricky as it's so exciting. However whenever I try and play she's just so bitey. I tried saying 'ah ah' and having a different tone then read that it was the wrong thing to do. I have tried ignoring her but that feels like allowing her and we're getting bitten to death. I read somewhere that when she's overly bitey she is tired so I've been putting her for a nap in her crate which she is fine with but I feel like she's in it all day. When I try and train her she just wants to bite and play. I don't know what I'm doing wrong! I'm determined to have a good, well mannered dog as she's a staffy and for now is tiny and gorgeous but soon will be a boisterous baby so I wanna get her trained well before then. We got her at 12 weeks and found out the 'accidental litter' owner, didn't give them any jabs so she's getting her 8 weeks at nearly 13 weeks and then the follow up after. I feel like she's missing out on being able to venture out to see noises and people due to this too. Would it be worth getting puppy classes?

Sorry for the long post!