It really depends what your budget is for the polishing kit. Autogeek puts together lots of different packages and obsessed garage offers offers a nice package as well if your budget allows. There are tons of options out there, it is an investment but picking up a good polisher like a rupes is worth it if you want to get into the polishing world. I have never used the torq but I think it's a good entry option for polishing if you do not want to pay for top tier polisher. You can get good results with just about any polisher out there if you have good technique.

Check out Griot’s Garage online for polishing kits.

Yes, you would want to stick with a dual orbit machine. Not sure which machine you are looking into but if it was me I would choose a smaller than 21mm orbit machine to pull double duty for sanding and polishing. Obsessed Garage has a few part series with Rupes on machine sanding, I think it contains a lot of valuable information about machine sanding and there are more parts about polishing as well.

21mm I'm referring to is the orbit size. The larger the orbit typically the quicker the correction but with sanding I would be afraid it would remove too much too quickly. The pad size either 3" or 5" just depends on what area you're working on. You could do everything with a 3" pad if you wanted just take longer in the larger open areas than a 5" pad to cover the entire surface area.