On highest difficulty you need to prepare very early for potentially (*) countering large rebel fleets with huge amounts of bombers and strikecraft. For this you need 2-3 at least shipyards specialized in cruiser and capital ships production. And IPV1 and ASAP lancers and better fighters of your own to counter the masses of small enemy craft. So yes, you need the research starting early.

The easiest wayt to do this is to build one fleet of starting ships and ground units and blitz until you baslcally have the left half of the map at turn 40-50 and 30k or so at least income. Focus on building economy, shipyards and research structures until then. Avoid space stations at wothless worlds i.e. no space mines capability or high base income until much later. Then gradually fortify chokepoints on ground and start building massive fleets. With this kind of income research is not expensive, in my last playthrough I had most of it done at week 30-40 or so and mind you I did it much more slowly than others as I spent money on outposts on almost every world expecting raids (that never came except very few).

(*) Actually the huge enemy fleets never materialized as well as they did in previous mod versions so after turn 50 was really zzzz for me.

For easy/normal difficulty, you can pretty do what you want it should be difficult to lose as long as you learn along the way.

AI seems passive for at least the first 50 rounds, probably they need larger clusters and/or being more aggressive to other AI, as it is now it is ridiculous. As AI is reluctant to attack other AI neutral white worlds are great buffers or you can leave e.g. one black sun planet as buffer against a larger cluster of rebel planets, even blockading it with one gozanti to prevent them from building fleets. No attacks will come from that direction for a great while if ever making the game super easy even on highest difficulty, if you do it right. E.g. in my playthrough bascially I could keep most (90%) of the outlying worlds as empire (Kessel, Rothana) even fortifying them very late or not even fortifying at all yes the Kessel cluster undefended was never attacked lol

the devs have said they are improving this AI problem next patch ( not sure when its coming) along with other fixes and an attempt to improve AI fleet compositions

Muchos gracias Lord of Pain!!!