Not sure if I can link here but worth googling one of the f2p guides on You Tube as many of the popular and successful creators have 2nd f2p accounts.
From what I've watched AhnaldT101s 2nd account videos had some pretty impressive progress, iirc he swiftly (well relatively) got Executor and SEE which is a great start for f2p. His f2p playlist is called "New Player + F2P Galaxy of Heroes". From your link it seems you may have the basis for how many and him started in that you've got Phoenix and Empire at the start.
Regarding the credits bottleneck its tough early on but will naturally disappear as you progress, happy to be corrected but they (like a lot of early game resources) just need to be carefully spent, then as your various income streams improve one day you'll find they aren't a bottleneck at all and you have a huge excess.