Info about the current rate limits can be found here: https://letsencrypt.org/docs/rate-limits/
Renewals do count for the 20 certs per week per domain rate limit, yes. But there’s a renewal exemption: even if you’ve managed to the 20 certs per week limit, you actually can get a renewal certificate. You just need to have the set of domain names exactly equal to a previous certificate.
So for example, you could get 20 brand new certificates and, well, let’s say like, 100 renewal certificates on the same day. And 7 days later you can get another 20 brand new certificates.
Obviously, trouble would arise if you got like, 19 certificates, forgot about one, got 100 renewals and have to wait 7 days for that poor cert which was forgotten.