As far as the old campaigns : -- I would finish LightFall first if you havent. After you unlock strand, you have to earn Strand currency to unlock all the fragments, grenades, etc... so if you equip the strand subclass & go play the other campaigns with it, you'll be earning the Strand currencies at the same time. -- Then play at least the intro mission to Final Shape, so that you can unlock the bare minimum of the Prismatic subclass. You'll have to finish the campaign to unlock some post-campaign missions if you wanna get all the different supers & abilities... OR... you can just join someone who has the missions unlocked & play them to get the supers & abilities. Not sure if you actually need to own the campaign for this. But I've done it on alt characters, to not have to play the campaign on them. *As far as all the Prismatic Fragments, you will need to explore & grind public events on The Pale Heart to unlock all of these. Some are simpler than others, but I do believe you need to own Final Shape for all of this, as well as for the secret mission for the Exotic Class item ... Altho... if you grind the Halloween event enough to earn 2,500 candy, you can just unlock the Exotic Class item from Eva Labante, who will be in the tower till Nov 10. -- Beyond Light will give you the Stasis subclass -- Witch Queen doesnt give you a subclass, but doing some of the campaign will unlock the Relic in The Enclave. You can use it to craft certain Legendary & Exotic weapons with the specific perks that you want. If you've ever gotten a weapon with a red border/box around it, the pattern can be extracted so you can craft it.

You should definitely buy the final shape to get access to Prismatic. Other than that, unlock the stasis & strand subclasses if you haven't, & then check the portal to find activities that you may enjoy & to get better gear.

I came back for a total of 45 minutes and got a refund

First, get the new gear chest next to Zavala. Then I'd recommend running The Final Shape campaign to unlock Prismatic; Prismatic is super powerful (and super fun) so it's worth taking the time to unlock all the skills. Then you'll want to do the Edge of Fate campaign - do it on Normal mode, Legendary really isn't worth it. After that, dive into the Portal! You can also buy the campaign skips if you want and go straight to the Portal, but then you'll be missing out on a lot of what you paid for, and The Final Shape really is a good campaign. Edit: Oh, and welcome back!

Go see Zavala he will give you gear to level up to 300

You’ll get experience booster perks in Renegades if you don’t go over level 30 on the season reward track. Depending on how much you intend to play, keep an eye on that. Pick up the chest in the tower by Zavala that should boost you to level 300 and get higher tier drops saving you from some garbage stuff. If final shape is cheap, I’d pick it up so you can get prismatic. Edge of fate campaign isn’t necessary for anything unless you want the story and access to a few mediocre guns. Raid is also included with EoF so if you raid, then you’ll need it. Hit the portal and grind. Then grind some more.

If you are playing on a PlayStation and have at least playstation plus extra, you can get all contents apart from a few dungeons up to the current expansion (edge of fate) for free. I'm led to believe it's pretty cheap on Xbox and steam, too.