How aggressive should you be in the laning phase (level 1-8 ish) with you spells? - ofc one person would get ring of the teacher for the mana regen, but like...i never know how much I should be harrasing during that phase.

how can we tell you just from this?
it all depends on your hero, your enemy, your enemy's items, and so on.

if stronger lane
more regen
lane advantage

super aggressive

Its not very simple to just say "use 25% of your mana at all times" You want to get the enemy to a point where you can combo kill them with your partner. this takes practice to know where that zone is.

Even better than killing them is freezing them out of the lane completely, making sure they don't receive neither experience nor farm

yep, sadly only few ppl know this!