The High-Tier and Sector X content in v. Angry Koala is mostly unfinished, there are no more bosses to defeat to unlock the next 6 Tiers after Sector X has been unlocked. We should assume that there will be additional bosses in the game and character progression could be much more difficult than it is currently.

Since you only need Aegisalt bars for the Aegisalt tech upgrade, and you would need 67 bars to craft armor, it's beneficial to skip the Aegisalt armor set and go straight through the tech upgrade to Ferozium. Once you have this, you can combine Aegisalt bars and coal to make Ferozium and craft that armor set. The same holds true for the next set of upgrades, skip Cerulium armor set, go straight to Violium gear. And of course you can skip Rubium gear and go straight to Impervium. This will help save some time. If you mine through the solid parts of the planet you can pretty much avoid most encounters with underground monsters, just try to stay out of the larger cavity areas. By the time you reach Sector X you should be able to have one of the powered drills to replace your pickaxe.

Chucklefish developers have talked about imposing a fog of war effect on the Sector Starmaps, and then requiring a certain amount of exploration in order to unlock travel to the next Sector. Currently the sector maps are immense and there are literally hundreds of star systems with multiple landable planets and asteroid belts. Imposing a fog of war effect would limit the number of star systems available to travel to within a much smaller region of the map, traveling to other star systems would then reveal more of the sector map.

The developers have also talked about having a range of difficulty levels within each Sector, indeed we saw this setup in the original version of the beta release where there we're 10 planet levels per sector. As a general rule-of-thumb there should be more ores available on higher difficulty planets, whereas your starting planets tend to be ore poor.