I'm thinking about buying some of Mel's Miniatures custom squadrons, but you do you use for bases and cardboard? I guess I can use bases from my other squadrons, but that doesnt solve the cardboard issue.

I use spare plastic bases from my collection. I have so many TIE fighters I really don't need more than 8 in a list and painted a few more differently to represent the Aces.

For the card discs you could print some off from the internet (like Kuat Drive Yards) or make some yourself on a computer. Print them off on paper then cut out and PVA glue them onto unneeded TIE Fighter discs. When dry use some black paint to touch up the edges then give them a protected varnish like Games Workshop's Purity seal or 'Ard Coat.

If you are a complete computer no hoper you can just buy some black paint and block out a TIE disc or X-Wing disc depending on how many hull you need. Transfer Decals and white/red paint could then add extra hull or Escort, Swarm or Bomber symbols.