Most npc turn in items are safe to delete, if for no other reason than the fact you can just get them again to do the heart.
If you are likely to play mostly one character (I do so) investing in bigger bags might be a good idea. Just be aware that inventory management is half of this game. It’s just how ANET does things unfortunately.
About the lvl 80 boost: you can use it and it teleports you to a lvl 80 zone and lets you try the profession before confirming it’s use. If you don’t like how revenant plays, you can just revert and try a different profession.