You don't need to reinstall SQL. So you have a lab at home that has a AD, and this VM is domain joined right? So you have domain admin role, you can create a single service account, and grant it local admin privilege's on that one VM and maybe even give it SA access to SQL (go into SQL management studio, go to security, logins, add an account, select the service account from the domain, and give it SA role). When you install SCOM, use another elevated account, and or log on with the service account and perform the install with it. The only issue you might run into is when setting SPNs, which you can address after the fact.
You shouldn't need to reinstall SQL. Having said that go into SQL management studio and if you have ops manager db and the ops manager dw, delete those databases, before trying to reinstall.
If you have SRS installed and it created the report server db and temp db, then you might have to go into the SCOM install tools folder and run something called srsreset (something like that). I had an issue installing reporting in the past, and SCOM, if it fails to install reporting, it can fowl up the report server, so you have to do a reset, and they have a tool you can use to do that.
I run a all in one in our environment. I use, not best practice, one service account for everything, to be replaced by gMSA soon. You can set this up using one service account.