As a general rule, rinks are a bit quieter during the day and I knew a lot of adults at my last rink that would practice on the public sessions in the day after they'd dropped their kids off. Your mileage may vary depending on your rink, but I've been to some VERY quiet day sessions.
Finding your own coach is something I'll let others chip in on.
In terms of progression beyond level 8, you're correct in thinking there are a Skate Star Bronze-Gold series of levels that you can do in Ice Dance, Free Skating, Synchro or Pair Free Skating (separate Bronze-Gold certificates for each discipline). If you'd like to look ahead then you can find the elements for each of those levels
here - the tabs down the left let you select the different disciplines. A lot of adults at my current rink tend to do both the Free Skating and Ice Dance Bronze-Gold, but it's really just whatever you feel interests you most - a coach would be able to guide you a bit more in person.
After the Bronze-Gold then you can move into the NISA test levels, where external examiners are brought in to assess you (rather than just being assessed by your coach). Whether you choose to do this is, again, entirely up to your own level of interest. You can see the test manuals for those levels at
this link, but as adults doing the sport then the certificates for achieving these won't change anything about your learning other than provide recognition of your work. Some people like the continual goal, but it's worth noting that they're a little more stressful because of the external assessment factor, which some people don't like. If you plan to do competitions then the NISA certificates are one way of meeting the entry requirements for some adult competitions, but there're other ways too. Otherwise that's it for the tests.
Hope that helps