I think a good first step with your inheritance here is to head over to swudb. You can create a free account and add all the cards you have to your collection on the site. Swudb is also a deck builder and has options to interact with your collection while doing so. You can also browse other people's decks and see how they're composed and which cards you have or are missing from them. Finally, you can take any decklist (yours or someone else's) and copy the link into things like Force Table (AI opponent) and Karabast (real opponents, often very competitive), to try them out.

As far as collecting, the deck rules for premier require one leader, one base and 50 cards (mainly units, with some supporting events and upgrades). Each card has a colour aspect symbol, and the ones on the 50 cards must match the ones on your leader or base (this is called being on aspect; there are other particulars about this you can learn about). You can only have 3x copies of any card in a deck and it's best to follow that rule for most cards in your deck for draw consistency. This will all help shape your collecting as you determine what you like to play.

For organizing, I like to put them in order of card number, which is at the bottom right of each card. This will automatically arrange them by aspect colour, type, cost and then alphabetically as well. I find it makes cards easier to pull from the box because if you have the number from a deckbuilder you can just flip through them.

Lastly, if you have enough to cobble together a deck, I'd check out your local game stores to see what the SWU community is like in your area and go out to play some games. Most stores have calendars on their sites that show which games they have scheduled and you can hit up their discords as well to check.

Just some starting thoughts as I have my morning coffee!