The bare minimum?

ok well I wanted to start a 20g long reef over christmas break but I really have a budget of about $500. For that amount I could get a reef-ready 20g long, a 10g (sump), glass for baffles, all the wood for the stand, two koralia 425, 20lbs for fiji pink sand, 33lbs of dryrock, and three 60degree PAR30 LED from boostled+fixtures.

Do I need anything else?

 

A skimmer would be a big help but you won't need it until the cycle is complete. Also no need to turn on your lights while cycling.

 

Also a thermometer, a heater and a refractometer to test your specific gravity.

 

I forgot to list those, I am going to buy my water from a reputable LFS by my house. Do I need a skimmer right away if I have a fuge with chaeto?

 

no - and you dont want to throw the chaeto in right away. I would suggest letting your tank cycle with just water, sand, and rock - and do not use any lighting cycle during your tank cycle.

 

Test the water from the LFS for nitrates and phosphates. Not all change their ro/di filters often enough.

 

If you have fuge with a DSB then start the DSB with the fuge now. Just hold off on the chaeto for now.

 

+1 to this. I did this with my previous two builds. I started the fuge up and had it running while I was able to build up the rest of my tank to my liking. Then once the whole tank is up, it has a solid base of biological filtration to allow you to build up slow from there. At least this is my theory anyways.

 

Heater, skimmer, return pump, plumbing parts, test kits, silicone for the baffles, carbon, cost of RO/DI for tops offs or an RO/DI unit, ATO (not completely necessary, but highly recommended). That's all I can think of for now, although I'm sure there are other things I've missed.