CMYK Printing - Tips and Tricks?

Hello everyone, I'm looking for tips for CMYK printing. The reason why is this is a service I would like to offer to new clients. Also it's a skill that I've always wanted to have, especially for my own merch. Any help would be greatly appreciated :)

1.) Plastisol or Water Based?

2.) Color Separating Tutorial?

3.) Are you charging significantly more for CMYK?

1 - I've always used plastisol ink, but I'm curious if a water-based ink would be better for something like CMYK. In your shop what ink are you using?

2 - I would like to say I'm pretty good at photoshop. After watching some YouTube tutorials I feel like this actually might be the easiest part for me. Although if you have a go-to tutorial for color separation, I'm open ears.

3 - I understand talking price is kind of a taboo thing here. I just would like some guidance in this area. Like are y'all significantly charging more for CMYK process garments compared to a job that just had 4 colors?

Like I said before any help in this would be greatly appreciated!