im not sure im going to much help here, as i havent had a super successful time with ivf yet... but:

i have been told that once you are successful with ivf, it is the same as any other pregnancy, you are not deemed high risk etc. just bc of ivf. generally you will have a couple of early scans (somewhere in between the 6-8 week mark), to check for viability and make sure everything is progressing 'normally'. i havent been past this point, so cant comment on further scans, but im fairly sure you are released to an OB around this time (maybe even 9 weeks? someone who has actually been this far can correct me, please!). monthly scans might be performed if there were concerns with the viability scans.
i have not heard that you are at risk of prem baby/babies with ivf or subsequent pregnancies after ivf.

hopefully some of the other ladies with more experience post-ivf can pop in and give you some info.