newbie questions on looting and currency

I'm soloing, and essentially my question is: what loot should I pick up to vendor?
I noticed that picking up all blue items, identifying them and then selling them seems to loose currency in the long run, you don't find enough wisdom scroll to identify everything and the average sale price for a blue is less than 5 alt shards, which is the vendor price for a wisdom scroll. Selling them un-ided works, if you do it for everything I think you will run out of portals, but that seems too tedious anyway.
So currently I pick up:
things I think I might be able to use
all scrolls and orbs
rares, identify and then sell
uniques, currently all stored
items with three colour linked sockets for the chromatic orbs
fully 4-linked helmets and boots, they might have some player trading value?
full 5-linked items, player trading value?
6 socket items for vendoring once they start showing up
all skill gems, although most of them seem useless?
potions that are either at usable level, or have quality/ magic for vendor recipes

I've also been keeping all orbs as I got them, without trading/vendoring them into different currency types.

Any tips and strategies appreciated.

I still pick up all jewelry/gems to vendor for scraps. A one square item is worth the space, and might give you an alch shard if blue. 2x1 or 1x2 whites are a coin toss. Sometimes I vendor them, and sometimes I leave them.

I save the quality armor and weapons for the 40% recipe, though it's probably irrational at this point. I hope they up the usefulness of quality in the linking process. It really is barely noticeable.

I save whites that are good "chance" material... currently engraved wands. If you trade for items, you don't need these. But I don't trade, so to get my sought after Midnight Bargain, I chance every engraved wand I find.

Most uniques are trash or serve lvling purposes, no need for hoarding them unless you have several stash tabs at your disposal and are going to run a big shop.

5L are usually 5-10c but that depends on the ilvl. 6S can be vendored for almost a free Chaos Orb.

Majority of gems are useless and go for alch/several alts. Those valuable include CWDT, CoC, Multistrike, GMP, LMP, LL, Chain, Empower.

If your soloing and planing on not trading , or trading as little as u can , deffinatly look up all the vendor recipes. They are very usefull. espeicaly past 60 when u can start to farm chaos orbs. but up till then they still are very handy.

Other than that u seem to have the right idea.

Only 1 thing i would add is in levels 72 and over i ususaly ID all the rares and toss out whats junk and only keep sellers/ wight items for crafting . In a party in maps it's important to keep room in your pack for large amounts of drops in a hurry. You never know when u may get a shavrons drop , and people have gone to pick them up and had them bounce out dew to a full pack haha

fully 4-linked helmets and boots, they might have some player trading value?
They don't. 4Ls are much too common.
full 5-linked items, player trading value?
Depends on the level-requirement and the itemlevel. But I'd keep all 5Ls just out of principle.
all skill gems, although most of them seem useless?
GGG plans to introduce proper gem sinks somewhen in the next weeks/months/years/decades/millennia ...
potions that are either at usable level, or have quality/ magic for vendor recipes
You can also pick up quality gear. Just like potions they can give you quality enhancing currency when vendored (40% combined). Those can be vendored for wisdoms as well.

With lots of IIQ you can afford to pick up lots of blues as well, without the risk of running out of wisdoms. With none, you might want to pick up only rares and the occasional 2x2 blue.
I've had good experiences just adapting on the fly. Sometimes picking up all blues to vendor them un-ID'd (and then vendor the resulting orbs for wisdoms), sometimes only rares.

Don't bother picking up blues, it's a waste of time.
Pick up all yellow/rare items, ID and vendor.
Pick up 6 socket items, vendor.
Pick up items with red-green-blue sockets linked, vendor.
Everytime you level up, check all vendors for RGB-link and 6s items, buy them and then vendor them.
Pick up all currency.
Pick up all superior gems.
Gems that anyone can get in a quest reward on Act 1 Normal, zero value. If you drop for example Empower, gems like that you pick up immediately.
5L items, well, depends on itemlevel and base items- if it's a low base item and low ilvl, I've given those away. If you drop a 5L ilvl 80 Astral Plate, that's a different ballgame.
Use vendor recipes, for example you can already use crappy uniques for 5x chance recipe.

Most low level uniques are extremely common and not worth keeping, some do have value however. You can check prices on poe xyz, take your time and learn what's valuable.

One thing wasn't mentioned: pick up and buy from vendors after leveling all white Stone Hammers, Rock Breakers and Gavels. They're used for chisel recipe. You can use them for chisel recipe or sell them. I think you would get 1 chaos for 5 of them.

I try to never go to town with an empty stash. This is what I do:

1. Pick up the small whites items so I can vendor and get wisdom scrolls.
2. Pick up blues and sell them for shards and eventually build up a stash of transmutes. Once I'm happy with my quantity of transmutes I sell them for 4 wisdom scrolls.
3. Pick up all items with quality to use in the 40% armourers and whetstone recipe.
4. I pick up all items with quality for the alchemy recipe. If I find a rare with quality and I know it won't be an upgrade i use it in the alchemy recipe.
5. I pick up 4L gear to use alchemys on for an, depending on how RNGesus wants to treat me, occasional upgrade. I keep them for the different color socket combinations just in case I want or need to try other skills. I also may want to use them on other builds.
6. I pick up all skill gems and iron rings they can be used in vendor recipes. Sometimes I give the gems away to new players too, just to help them level a little quicker.
7. I pick up all uniques to either use in the vendor recipes or give away to new players.

I play in a very slow and grinding type of way. This is easy for me to do in standard because I have a portal gem. In Ambush what I do to conserve portal scrolls is most of my farming is done in an area with a waypoint in it. After clearing a zone I place a portal next to the area with the most drops and I leave through the portal. When I want to return to the area I enter through the way point and run back to the portal and keep doing this until I've picked up everything that I want. The portal will never close as long as i get back before the timer runs out. If there is a waypoint near the beginning of a zone I use that waypoint to farm the previous zone. For example, I use thewaypoint for the Mud Flats to farm the Coast. I use the waypoint from the Cavern of Wrath to farm the Coves,etc. You have to make sure you have some sort of fast movement skill. I use leap slam or shield charge

As I said it's very slow and methodical. I have to do this because I play self-found. This is a basic outline to how I play
If you don't know the vendor recipes read up on them here:
pathofexile.gamepedia.com/Vendor_recipes#Crafting