Does the new one play like Master of Orion 3 or 2 etc? How are space battles done? Like 2 or 3 or different than both?

It could be an excellent game finally, but Wargaming.net has abandonned the game, needing patches.

So It's going to be like MoO3 and have to be fan fixed with mods etc?

Yes, but the mod compatibility is boring, and even modders tend to quit the game.
In theory, the best is to add Unofficial Code Patch and 5X-Lite, using the 5X-UCP Compatibility mod, but there was still too many bugs 6 months ago. Try here, maybe it's good now?:
https://www.nexusmods.com/masteroforionconquerthestars/mods/30
https://www.nexusmods.com/masteroforionconquerthestars/mods/42
https://www.nexusmods.com/masteroforionconquerthestars/mods/45
The very devs have decided to let modders do their own work, Wargaming.net is too poor.

I finally came back to old MOO2 (see mod thread here) then went to StarsInShadow.
http://moo2mod.com/
https://www.gog.com/games?devpub=ashdar_games