Welcome to the forum, Carlos.

You are going to love this site; lots of good people and the best XF resource anywhere!

Lots of mod possibilities, but they tend to be a bit pricey since these cars are mostly Mercedes under the skin. Keep an eye out for group buys. A cold air intake and good rubber were my first mods.

There are several places where the ECU can be sent for a reflash; not difficult, just a few days downtime for shipping.

If you have an NA XF, TVT does offer some nice packages, and they are quite active on this forum.
If you have an SRT, there are several shops that can help meet your needs.