If you plan to paint big surface or whole kit, then it would be better to prime first. If just small parts or minor detailings, it is unnecessary to prime, sanding is enough.
You could paint it with marker pen, hand paint using enamel bottle paint, spray can or airbrush painting. I just paint with marker pens for my first SD because my bottle paints are lacquer so not suitable for hand painting. You can check on my earlier post, SD DiaoChan to see the result.

You can either use the sangokuden marker pen set, other marker sets or you could just randomly buy the marker that you like. I would advice you to use Gundam Marker for small detailings, Tamiya marker for larger surface. Reason is Gundam Marker having smaller tip, if you paint large surface it will leave quite obvious brush stroke. Whereas Tamiya marker have bigger tip so it is more suitable for larger surace. Tamiya paint also have higher viscosity(resistance to flow) so if you paint on small details, the result will become very thick unless you extract the paint to paint tray, add some retarder or thinner then painted with brush.

Enamel paint is more suitable for larger surface hand painting compared to marker pens. But you need to have very fine brush(tamiya brush for example) to paint the small details on your SD kit. For larger surface you can use the fine brush that normally can be found in stationay store, but still hobby brush is better, depends on your budget. First of all, thin your paint with enamel thinner, after that paint your part layer by layer(thin layer) in one direction to reduce brush stroke and get a better finishing.

If you not confident with your hand painting skill and you not willing to give it a try or treat it as a practice, you could use spray can. I don't think there is much things to talk about spray can. Primer->Spray paint(also layer by layer)->Top coat. Some people like to do wet sanding after each layer of paint, well I don't do that because I'm lazy and not sure the purpose but I guess is to give better adhesion and smoother surface. I also don't use much spray can because I'm not familiar and skillful with it, and lazy to do masking.

Anyway, I strongly advice you to top coat your kit after you paint it to protect your paint. Flat, Semi-gloss, or Gloss is up to you, different people different preference. But I always use Gloss top coat for metalic paint so it will enhance the shiny surface whereas flat top coat will reduce the shiny surface of metalic paint, so no point to use flat top coat if you want shiny surface.

You could prime with Mr Hobby then paint with other brand paints, same for Tamiya primer. But don't use the primer from hardware shop, they are not suitable for ABS plastics. Wish you good luck for your first attempt on painting, and pardon me for long reply I just hope that I'm able to give some help and suggestion