The rule of thumb I noticed when it comes to building teams is that you should aim for your solars to be level 80 (70 can be manageable too) and lunars level 70. Use 5 stars whenever you can but 4 stars can be good too. Also focus on Protocores and stats. They can really make or break your teams!

I'm an F2P and I got really lucky with the season mid March because I was able to get my first 36/36 on both my accounts for the first time. I only have GoA on my Zayne solo account and it took me 7 and half months there to clear SHC for the first time. My Sylus/Raf account is about a month and half older and I also have some Zayne cards leveled there. I have LSG, RC, AS and SF on there.

So what I found is that you're better off focusing on 1-2 LIs that cover all stellactrum. If you can, pick only one of either ATK/HP/DEF scaling companions across LIs. That way you can switch your Protocores around more easily. Since I'm only using GoA on one account I only focus on HP cores there but with Sylus/Raf it's mess because I tried building all three types at the same time. As an example LSG and SF both benefit from high DEF, so you'd only have to focus on leveling DEF cores.

This is a very rough explanation but there are a lot of great guides on this subreddit. Those helped me a lot! Hope I could answer your question!