Looking at getting back into X-wing after a several year layoff. Would like to start with my son, and he's interested in Imperial. We have a few Imperial ships:

1.0 Core Set TIE's, TIE bomber, TIE Defender, Alpha Class Star Wing, and TIE Aggressor

Thoughts on what else we should pick up to get started? Thanks in advance.

imperials conversion kit out of the gates. bombers. bombers are good. 3 total at least. They hit hard with barrage rockets. Sprinkle in a punisher or two, tie-intercepter, a phantom and perhaps a lambda shuttle? That gives you quite a few aces options (whisper+deathrain,+redline or soontir+rexler+vader sort of deal) and u can also mix things up and play 3+ bombers with the defender or a lambda perhaps. Lt. sai the new shuttle pilot is gr8 but even Col. Jendon with bombers works.

More tie fighters, if you get imperial conversion kit get ties used for cheap online or at store.

Since you will need to pick up the new starter (for a damage deck) and likely the conversion kit, you have a pretty solid start. TIE mini swarms (4 ties) are not what they used to be, but with the Inferno squad characters, theey aren't bad. As da brown pointed out, bombers of all types, including the TIE bomber and the star wing, got a good boos in 2.0 (do not throw out your old bomb tokens!)

I am still new to being back after a long hiatus myself, but the TIE advanced seems to be really popular right now. With the Force rules, Vader in particular can bring a surprising amount of pain.

So short version, a TIE advanced, bomber and maybe punisher would be at the top of my list, but get the new rules and tool around for a bit first. He has a solid set of choices to start with.