There are some factors whether you'll have 6k gold or not in turn 100.
First, it depends on how fast your progress on adventuring tech. That's why lost libraries is primary focus, the ideal starting is get 2 lost library asap, if you can before turn 30, you already have 2 libraries built, if you can have more than 2, go for it. This is important, because enemy faction can steal many notables you spawned, simply because you can't open it but the enemy already have the tech to open it. The main source of gold are curgen hoard and treasure chest (both lv 2 and lv 3), curgen alone usually gives 600-800 gold, lv 2 chest 150-200 gold, lv 3 chest 400-600.
Second factor, also as important as the first, you must have high movement speed, so gives the +movement speed item to your sov and early champion asap (usually janusk, no other choice), 3 mov speed is ok, 4 is better, 5 is best. And because they remove organized trait from sov trait in 1.09, be prepared to be attacked frequently by neutral creatures (just run away if it happends), because you can't bring troops, not even summoned creatures as they'll seriously slow down your movement, which is a big impact, remember enemy can steal your notables (curgen, chests, etc), though you can also steal their's.
Third factor, your luck, well, how many curgen's hoard and treasure chests you get and how good their location depends on it, however most of the time they're near your teritorry or in neutral teritory if your progress in adventuring is nice and your sov have good movement (this is done at full enemy factions, ridiculous difficulty, large map). And curgen hoard and treasure chest doesn't always give gold, they sometimes gives crappy item such as destiny sliver or midnight stone. But, even at worst luck, at turn 100 you should get 3k-4k gold, i never get lower than 3k. Well, remember that you can also steal notables spawned by your enemies.
As for the armies at turn 180, it depends on play style and some factors too, like how many enemy's cities captured, do you already get dragons/drath, etc. I mean it's relative, the adventuring and all those gold are merely an opening, the rest is up to you. For me, my main army usually consist of the quest dragon (must get him before turn 150, then feed him all +atk books gained from notables), and probably 3-4 archers on my sov side. However this doesn't limit you to use another army (since your gold is abundant and those are merely opening), i mean you can use the heavy armor melee which cost very high and often need crystal, though what technologies you research also depends on play style and usually by turn 180 i neglect melee weapon and armor equipment, though magic equipment is an exception. Basically, it's like quantity vs quality thing, except you have the choice to use magic or not (combat and support spells).