Unsure start

[Zed26]

Is there limitations on what ship you can fly with which faction? Specifically can I fly a Zoners ship when I'm an Outcast?

You can fly just about any ship-ID combination as long as your ID lets you fly that class (transport, gunboat, cruiser, battleship). However, you may receive a reduction in your power core regeneration based roughly on the how the combination "fits". In your example, the table here the intersection of Outcast IDs and Zoner ships is a red cells, so your ship power would only regenerate at 10%. The only exception I can think of is the "Whale" Zoner Transport, where the infocard specifically says it can only be used with a Zoner ID.

If you want to fly a unique combination without a regeneration penalty, you can build some RP and apply for a Special Role Play.

See this post for more info on techcompat and shipcompat.

do I have to tag myself...

No tagging required, but you can do it to make yourself easily identifiable if you want.

I can just go RP a faction I want without joining a official faction...

Yes, you can be an independent character for most factions without joining their official group, but I'd recommend it once you feel comfortable. There are a few exceptions with unique IDs not for sale, but most have an open ID that's similar.