Felix,
If your Mini tactical looks like mine (you can check out my RedDot in the Gallery. Anyway if it looks like that you will probably don't need to anything as long as you have the Picantinny/Weaver Rails.
I have a RedDot on mine and love it. Took about 20 minutes to dial it in at 50 yards which was right on. I also added a laser, tac light, front Ruger folding handle, and muzzle brake.
If you go into gallery and find the post "my newest Mini 14" if it looks like that with all the rails you only have to make one decision and that is what RedDot you want. They range from around $50 to $400 for an Eotech RedDot. I chose mine based on price, reliability, how many reticles, illumination, and ease of installation and site adjustment.
If it does not have the rails and you have a tactical version of the Mini-14, the rails are sold all over and pretty easy to install.
Anyway, thats my two cents. If you could post a pic of your mini in the "Gallery" section it would make it easier to see what you are dealing with.... BTW mine is 580 series (the stock model; the way I bought it is my avatar)
Take Care