@Theotis im sure that you found out by now, but those are the montha for each step of the project .

What does it mean, on the orbital screen, in colonist migration the numbers > 5M | 7M | 5M | 7M? Before completing the half-cycle the colonists arrived on the planet, this bar is very confusing, can someone explain?

Don't use aerological scanners, just drop new landing sites. starting from the initial lander, go along the x or y axis to the farthest revealed tile and then go 6 or 7 unrevealed tiles out for the location of the next landing site. Every time you drop a lander on unrevealed tiles it generates resource nodes so that the landing site can become self sufficient. If you drop a landing site on a patch of revealed terrain it won't generate the resource nodes. Dropping lots of landing sites nearby allows for quick connection to your existing district, mitigating the need for additional factories at every location and helps get existing factories to 100% efficiency, as well as creating a surplus of goods. Only took 4 or so hours to get to 12 districts and 600 colonists on max difficulty doing it this way. No real issues other than getting to that first maintenance facility.

Build biodomes in high humidity areas to maximize growth of vegetation, also it doesnt seems to spread over roads

Don't add a New Lander to an area that has already been Areologically Scanned to be empty. When you land there, it'll still be empty, and y'll have a nice new lander with nothing to mine.

Instead, find an area nearby that has not been scanned yet. When you drop the lander down, the game will create random mineral deposits nearby, at least one of each that you need. Then you can start building a little network, just like you did with the very first lander.

Sure, it's not realistic, but hey! it's just a game, OK?

I have found that it is virtually impossible to always have the resources ready for all the factories.

Example:
As part of your initial colony, you create a steel factory. It requires 2 basic iron mines to operate at 100%. By the time you have a second mine (depending on RNG), the first one is very likely depleted or near depletion. So maybe you take to landing sites to fan out to get more iron. But then, to get that site up and running you have to build a steel factory. Now you have 2 steel factories that can never be satisfied.

Engineering research holds me back from actually playing the game

According to Javier Otaegui, dev:
"Each fully-manned research lab gives you a 5% boost, and it's a compound boost. This means that if you have 10 full manned RLs, the boost is not 50% but 62% (1.05 ^ 10)"
Source: https://discord.com/channels/261683801372098560/586574485528903683/816805943911645214

Apparently having fully staffed and supplied research outpost gives you a research bonus of 5%. So a few of them might be actually useful. Kind of wish I knew that before getting all the way to Stage 5.

@OpiticalDuck2
There is nothing wrong with the lander you just have to build in the same order as start. And select level 1 on mines and factories. Since aluminum mine is the first thing you put down you shouldn't have a problem with getting aluminum. If you set them up with the last building you build is a hyper-loop they are easy to connect to the rest of the colony. Drop a hyper-loop first to get the range then the lander near it, remove loop, and build like it's the first time again. Power is the only thing that is not connected just have to look for the power out icon then add more. I think this is a slower way to expand but it's great for the hard to reach areas. And the people will travel to the research sites just have the food processing going before you drop one.