Help & Tips?

I got the game a couple of days ago, and I've already played 33 hours, got even an Outrider set but I got a couple of questions.

I'm the "Investige Floran" mission and have almost done it, I'm like at 60% on the progress bar of the quest but I've like on 7 different forest planet and can't find anything new..

Also, I've got like 12 upgrade modules but don't know how to upgrade the ship, I've looked it up and I don't have a crew so I'd have to buy a fake license, but the guy who's supposed to sell it to me isn't at the outpost (do you have to unlock it?)...

Last thing, I'd like to find more mech parts and the famous drill spear, but I've been on gentle, temperate and radioactive systems and can't get any (anomalies and ships too), I've found the USCM body, Hopper legs and a missile launcher but that's it.

I've also heard about tiers, how much harder are tiers 4 to 6?

As I said I got the outrider set and a durasteel sword but that's about it.

I'd also kike to find a rebel set (for appearance only, but I've only got the hoodie) but I can't find it or craft it either.

 

Just keep searching for it. I believe it is not that hard. It took dozens of planet before I can finished the quest.

 

You must have been unlucky and didn't find items that unlock a lot of progress.
About the ship upgrades, the legit way to get licences is to recruit a crew, by completing quests from the same npc's. You get a licence for every 2 crew members you get.
Mech parts are usually found at the "center" of an encounter, as rewards. But if you want a particular weapon, you should check its tier on the wiki, you will have more chances to find one in missions with the difficulty that matches.
I would say there is a big leap between tier 4 and 5, since you have to chose with tier 5 armors to have a boost in one stat (plus the fact that they are still better than tier 4 armor without the boost), but I think the difference between tier 5 and 6 should be the same than let's say tier 3 and 4.
What race do you play ? I think the rebel set is an Apex armor set, so only them can craft it. But you can find Apex merchants that sell pieces of the set, I guess it's also linked to tier planet so check on planet that matches the rebel set tier.