Personally, when I come back to San MMO after a long time away, I like to start with a brand new character for exactly that reason: it gives me time to figure out which crap in my inventory is actually worth anything.

If you want a quick way to clean out your inventory that probably won't get rid of anything too important, type "trophy" into the inventory search bar and ditch all that stuff. Use the 80 boost on a new character; it doesn't lock you out of your personal story. If you want to keep going, use the wiki. In case you're not aware, you can link an item in game by shift -clicking it. If you type /wiki in the chat and then link the item, it'll bring up your browser with a wiki link to the relevant page. The wiki will often tell you if the item is worth having on to.

There is a free 24 slot bag that you can claim for subscibing the newsletter, every little bit helps :) https://www.guildwars2.com/en/news/free-24-slot-bag-with-newsletters/

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.

Bank space in this game is way too small... I do need to keep one character as extra bank space. I haven't played enough in a while to give any actual tips for cleaning inventory, but I hope you haven't kept all the heart quest items! XD

I have a hoarding problem too, so I will share a few tips.

• As others have said, the wiki is really good in this game, and can be launched from the chat. If you're wondering how useful something is, the wiki page will have a list of aquisition methods so you can verify if you can get another copy later. Also good for clearing out the turn in to npc items, as it tells you where to find them.
• For things that aren't account/soul bound, I usually just sell them on the trading post if they aren't immediately useful. If you need it again, just buy one back for a slight premium. I think of it like a storage unit.
• If you don't want to do the above, look into creating a personal guild just for guild storage. Again, this only works for stuff that isn't bound and takes some up front work and money, but in terms of cost per slot, it is very efficient.
• Mule characters are a common if cumbersome solution to this. Just create a new character and offload stuff through your bank. Anything you need again later they can send back.
• I would recommend upgrading to 18 slot bags when they seem affordable. Keep in mind you get most of your money back from selling your old bags on the trading post, so don't worry about settling for something affordable now. There are also some achievements and thing that reward large bags.
• Most vendors have a sell tab with a button to sell all junk. Use this, as there is no other use for those items. Items that mention "this has no value outside of a collection" or similar can also be safely sold to an npc, as they are added to the collection on aquisition. If they are leftovers for renown hearts or similar, just delete them.
• If you have excess for non-ascended crafting components, I would go to the bank and sell off the stack and repeat the next time it gets full. Ascended crafting mats are unfortunately account bound but you can get rid of these with gobblers/converters for a reward if you want to get those.
• If you haven't already, get familiar with two buttons in your inventory: deposit all materials and compact. The former moves stuff to its dedicated slot in your bank and the latter gets rid of gaps in your bags so new stuff goes to the bottom. The dedicated slot is also accessed for crafting too..
• Rare/yellow gear and below can generally be salvaged (or sold to the trading post) without worry, since they are common enough random drops. There might be some bound gear from your initial character creation, leveling, or achievements that are technically unique, but they are replaceable with much better things anyway. Any unique skins would be granted on salvage/aquisition. Again, you can use the wiki if you want to be sure.

https://gw.zweistein.cz/gw2stacks/ is very useful for this.

I advise that you don't follow it 100% blindly, but it's very helpful. Note that you will need to create a (read-only) API key from your account page at https://account.arena.net/applications