I just got my first few ships for Christmas
Starter
Falcon
Hwk-290
Tie bomber
B-wing
I found one of the $20 starters at target and picked that up
I'm looking to fill put my fleet a bit more is it worth it to just but one of everything I don't have? The lambda seemed a little specialized for casual play.
Also are the expansion xwing and tie worth picking up if I already have 2 starters?
The expansion X and TIE are worth it if you want more pilots, which certainly add variety to the game. They also have a couple of decent upgrade cards, so I'd say yes, but only buy one of each.
As for the shuttle, it has some components you could use on all the craft you currently have. It's also a difficult, but still very fun, craft to have on the table. It takes skill to use them, so I could argue either way. If you're really not sure on your purchases, I'd say go to the X-Wing Wikia and you'll get a breakdown of all the included stuff with the sets. Hope this helps!
The shuttle is a great craft and can be a lot of fun to fly and be a powerful addion. I'm the largest proponent of the craft right now. However, I'm not sure it's right for you just yet. It requires certain upgrades (Engine Upgrade, Fire Control System, Gunner) to be powerful, and requires a bit of skill to fly well. So, while I would certainly suggest you get one, especially if you like the idea of this beast, it's not one I would recommend adding to your fleet just yet.
Right now, you have 4 TIE Fighters and 1 TIE Bomber for imperials. If you get an additional TIE Fighter and the Lamdba, you don't have a lot of options for a 100 point Imperial list. The one I would urge you to pick up is the Firespray. It's an iconic craft, quite powerful, and a lot of fun to fly. It'll give you another bomb option as well as the Gunner upgrade card, which means you'll have the last card you need for the best Lamdba combo as well as to make the standard Han Shoots First list.
The X-wing and TIE expansions are must haves for the pilots.
Buy the shuttle last. If you want a large imperial ship get Slave 1.
I agree the Firespray (Slave I) is a much better purchase over the shuttle, IMO. It's more playable, and Stealth Upgrade is good for lots of different ships, in addition to being pretty awesome to fly.
And pick up an extra Core Set. You'll get more value for the money (3 ships, dices and Damage Deck) for a very low price, then add a couple of TIE&X-Wing expansions and 1-2 Y-Wings and a Firespray