Grab Siyalatas and lvl It up to lvl 16 (becomes less efficient after that), then grab Liberatus and lvl it us X amount of times. Makes clearing out the first 200 lvls go by fast. Morgulis is good to drop souls into due to the extra 1% dmg increase/soul. (Also helps those itchy fingers from spending them on needless Ancients).
An issue with the gold on amount on the investment bar. You can go up to the high lvls (I.e. 150) fight the guy, die, then collect after the fight and earn a lot of money just from dying to the mob. Can max out Pots and Upgrades in 2 mins if done like this. Just so the game dev knows and can fix it!