I just want to play offline single player, but I heard there are so many bugs that can actually ruin your game, lost save files, crashes that set you back 30+ mins etc.
Is it safe to play single player after the most recent patches?

Yes, its wayyyyy more stable now even though there might be 1 or crashes here and there but not as often as when it was launched
Both offline and online are safe to play, no lost files whatsoever

Thank you! Do you have any build/playstyle recommendations if I want to get as close to the Path of Exile Blow-Up-The-Screen type stuff?

Really depends on what you like to play, melee or mage.
As of this patch arctic spear is the strongest but they will nerf/patch it soon as its doing way more dmg than intended
Pure mage is 2nd strongest in my opinion and for melee, BE (bleeding edge) still best. Others are turrets with havoc orb.
Gunslinger is 1 of the meta builds but in terms of speed, its the slowest of them all.

Don't go for bow, they're not viable as of yet.

Here are links to all the best meta builds thats updated: https://wolcen-universe.com/users/xgen74

Thank you