Picking a printer is a little troublesome, be sure to read reviews. As for modeling, there are a few things to keep in mind, mainly that everything you build needs supports, it can’t print on air. Most printers can print from one support point to another as long as they’re not too far away, but you need to model everything so that it grows from the ground up.
The thing that trips up most new people is that the object must be a single, solid surface. This means that there can’t be any surfaces within the model, and no gaps in the surface.
There are a lot of tutorials online. If you’re familiar with 3D modeling then it should be pretty easy to adjust to. If you’re not, then it’ll be a pretty difficult road to get to go modeling for 3D printing.