New player here, I'll share what I have learned.
Exploration/Surveying is a big investment. I thought it would be just sending some scouts. My first survey fleet is usually 2 Shepherds, a few buffalo/Mules, and something to carry crew. Targets are to have 150 machinery along with 850+ crew. This is so I dont have to skip gas giants. I try to carry 1-2k supplies - ideally with room left for loot, but usually not much. Each planet you survey empties your hold, so you can come back for high value stuff on your way back to refuel. Eventually you will come across massive and high value loot hauls, so it pays off.
The shepherds reduce the amount of supplies and machinery required, and you will need a tanker too. Dram is fine. This fleet can survey a whole quadrant at once (efficient). You may not be able to field something that hits those targets so even dropping to 500 supplies is fine. You can use much less machinery and crew if you skip gas giants too. They are not very different, and you only need volatiles from them, which can be found elsewhere. Feel free to skip gas giants at first.
As for colonies, biggest tip is keep the hazard rating low if you want them making money early. Anything with ore bonus (ideally rare ore) or any volatiles is free money if hazard rating is low. Id go 175% and lower. Dont set up high maintenance industry on high hazard planets - they are best for resource gathering, not manufacturing. Something like refining or light industry for later. Fuel production industry pays big, but dont overbuild as the market is easy to saturate.
That being said, dont be afraid to colonise, you dont need class 5 planets, i've made millions from some class 3s. You dont need much to get started, I dropped mine at $250k, and was never in danger of running out of cash. Get your defenses up after the first industry, the AI will send stuff pretty quick but if you prioritise defenses first you will be safe. I got pirates non-hostile first, but your auto built colony fleets are going to get pretty good so I wouldnt be too worried if you have them hostile.
Also be aware that 1 larger cargo ship/tanker is always less costly to run than several smaller ones. If 4 mules is what you need to carry stuff, its time for a colossus. The slower burn speed can be countered. Even capital class logistic ships can be as fast as burn 10/20 with the right (story point built-in) hull mods + talents/tug ship.
I was overwhelmed at first, but just get in there and do it. It fits together very fast when you 'get' it.