So just something I've been thinking about:

What ships should a player own multiples of besides the obvious TIEs, Xwings, Bwings, IG-2000?

EVERYTHING!

2 of everything then 2 more.

THE PLASTIC CRACK ADDICTION ONLY GETS WORSE!

All the things?

(I need to update with all the new things)

Ties and Z-95s are fun for swarming. I've got 7 of each not counting the new FOs. Five Khiraxz in a squad are cool. It all depends on what you like to fly and how badly addicted you are to the game.

You'll probably want many (4+) of

Tie fighters

Tie FOs

Z 95

Scyk interceptors (debateable, they aren't the greatest ship right now, there will probably be an aces pack at some point)

Aggressors if you play epic and want to run 4 IG-2000s

Any small ship you like a lot

Probably only want 1 of

Hwk

Phantom

Defender

E wing

Star viper

Any large ship you don't really like a lot

Huge ships

Everything else it is entirely reasonable to get 2-3 of

If you intend to play in tournaments, adjust numbers for difficult to get upgrade cards

Bit of general advice. FFG releases "ace packs" that include previously released ships with new pilots. It is frequently not necessary to run out and get a full set of a given ship right away because they will probably release a new expansion with the old ship sooner or later. Good example is the scyk. If you like the ship, you might be tempted to go out and get 5 of them right away, but FFG will probably release an aces pack that includes at least one more of them eventually, then you might end up with more than you want. Happened to a lot of people with the TIE interceptors back when imperial aces came out. Patience will keep you from spending way more than you want to.

At least until the addiction kicks in full strength and you end up with 6 of every ship.

Just look at my sig line! IIRC, the only singles I own are, Raider, Tantive and YV-666. I can see a second of each of those eventually too! I ordered two GOZANTIs right away because I know I want three eventually!

First starting point: if a ship appears in more than one expansion, get all the expansions it appears in. This maximizes your diversity of pilots and upgrades.

Second: never buy more copies of a ship than can fit in a 100 point squad unless you have a good reason for it, such as desperately needing more copies of a certain upgrade for tournament play, or wanting to do crazy Epic games.

Third: Beyond that, almost every small ship can be fun to have two or more of. Only exception in my opinion is the HWK - there are very few lists that meaningfully use more than one HWK-290.

Fourth: Large ships are generally not worth having two of except the Aggressor. Two of any Large ship could be ok if you have a reason for it. Three of a kind is silly.

Fifth: You really only need one of each Huge ship unless you want to do the triple transport mission and are supplying all your own ships, or love flying two transports in Epic games.

Does it count as multiples of the "same" ship when you buy it through different expansions? I'd say "no" which means that as long as you are part of the "one of everything" group the list of additional ships you could really use is pretty small.

Z-95 Expansion: Even with Most Wanted you need more for rebel use.

TIE Fighter??: Although the Epic carrier including two more would leave you with a base of five which is enough for many things.

After this I think you're looking at multiples of the same ship mostly when you start looking at specific squadrons. Bro-brothers has an obvious requirement and while you may have seen early squadrons with two Falcons and perhaps three Firespray there are similar options without all of those repeats.

https://community.fantasyflightgames.com/user/212948-joe-boss-red-seven/

You definitely want three hawks to run all three scum pilots in a build...

As a general rule if you want it buy two, if you don't buy one.

I limit myself to no more than 2 of the same set/expansion pack. As for what to get multiples of look at my sig with the exception of Imperial Aces, you don't need any more than 1 of those.

I have 5 Y-Wings because... I like Y-Wings, and before TLTs were a thing, bring 4-5 Y-Wings to a game made people do a double take.

What ever you'd have fun with really... though logically, anything you think you can field multiple generics of. Things like a Kihraxz, Z-95, B-wing.

But really liking the stuff you get is what the end result should be.

I am fairly new to the game, but have grabbed pretty much one of everything for the Rebels and Imperials. I have skipped Scumm so far. The only double to date is a spare Y-wing... Because I honestly screwed up an order. I do want to get a second set of each core set (when the price is right) because I love the X-wings and my son loves swarming me with Ties.

I would also say to get more of what you like.

Eventually, I see myself doubling up on most of the small ships.