seir: The battle mechanics are definitely different between SF and SC, and the way you explore planets is also different. I personally like SF better on both fronts. The similarities between both SFs and SC2 are the overall feel of the games in how you explore and interact with aliens--and this is the best part of the games! The best way to see how they're similar and different is to play them.
While it technically doesn't really matter if you play SF or SC first, since they're unrelated to each other, I would recommend playing SF first. Like many other space sims, Star Control was definitely influenced by Star Flight, so if you play Star Flight first, you can better appreciate the impact it had on other space games that followed. Star Flight had a very big impact in the gaming industry.
Within the Star Flight series, definitely play SF1 before SF2. There are story elements in SF2 that you will definitely not fully grasp or appreciate if you don't play SF1 first.
For Star Control, feel free to skip Star Control 1 and go straight to Star Control 2 if you're not finding SC1 enjoyable--that's what I did. SC1 is basically just battles. While SC2 has the same battle system as SC1, it also has real story and exploration, which make it a far far better game. It's the story and exploration in SC2 that draw you in and encourage you to keep playing, NOT the battle system.
Of course, if you find that you really like the battle system in SC1, then you'll probably have a different view on SC1 than me. But story-wise, there's not much there so no problems skipping it if you want.
I've replayed both SF's a few times over the past 20+ years (I'm replaying SF2 now in fact). I've replayed SC2 a couple times as well. I gave SC1 two chances and stopped playing both times (once before SC2 and once again after), and I've never felt the need to give it a third chance.
SC3 is also worth playing, though, I'd play SC2 before SC3.
Two tips for Star Flight:
1. Write notes, trust me! They don't need to be extensive, basically just notes about places that you learn about through notices and conversations, which you might want to get to later--your notes will be your best way of getting to that info when you need it.
2. Read the manuals for the games! There is important story in the first part of each game's manual (the briefings). After that, even in the manual proper, the information is useful for a first time player and is actually somewhat interesting, and on top of that there are scattered quotes from other captains that are entertaining and sometimes useful.
Also, DON'T,
I repeat DO NOT, read the SF2 manual before playing through SF1--It has BIG BIG BIG story spoilers for SF1 if you do.
Actually, the battle system is really robust and solid on its own.