I buy 6" sanding pads from harbor freight and they work fine. They may not last as long as higher quality stuff but they last me a while. There's 50 in a box for like $10. It's not a big deal.
Harbor freight does sell a 2" dual action sander. I didn't buy it. It might use sticky pads but I'm not sure. i have the angle grinder, same one in the pic I linked. I use HF 2" and 3" pads with the discs they sell. They work ok as well. I tried sticky on them but it didn't work, that's before I found out about twist lock.
Make sure that compressor you are buying is going to meet your needs. I brother has a newer 5peak HP 120v 30 gallon oil-less compressor. It's stupid slow and can't keep up with my DA, about 1-2 min of use before I have to completely stop. I have a 20ga 5hp belt driven 220v craftsman compressor that is amazing. It can refill the tank faster than I can use it. It sits at 150psi, when it gets to 120psi, the motor kicks on, and it takes about 5 min of constant use to drain to 100 psi, and never gets below that. I can run continuous.
Peak HP, tank size, etc, any one factor can't judge the performance of a compressor. A big tank doesn't mean it'd going to run that tool for extended periods. Make sure you get something that can crank out some serious power to get that tank full again. You have a 25ga tank and a weak motor and you will quickly find that 25ga isn't very much.
Oh, lastly, if you are having problems with pads sticking, clean the disc with acetone and let it dry before you put the pad on. You should not have any issues with the HF 6" DA and HF pads. However, you are not going to get a 80 grit sticky pad to stay on a angle grinder turning 16,000 RPM. You might be able to get a 180 grit sticky pad to stay on a 2" DA since it turns as a slightly lower RPM, but otherwise, you need twistlock, and that has nothing to do with HF.