Welcome to the insanity............err, hobby

The Kadet Seniorita is an excellent plane. You will like the plane. It is a gentle, stable flyer.

The biggest advantage to building your plane instead of an ARF is that you not only KNOW how it was built (quality of construction), but when the inevitable happens, you will have the knowledge/skill to repair it.

If your budget allows, get a 2.4 radio, preferably a 6 (or more channel) computer radio.

As for an engine, the most user friendly engines I have found (in no particular order) are OS, Thunder Tiger and Evolution. By user friendly I mean that 99%+ will run decently right out of the box, require minimal break in and have good power.

Just starting out I would avoid the Tower engine. Magnum engines have mixed reviews and MDS, in the under 1.60 range, stay away from. MDS have a couple of nicknames that are appropriate - Mostly Don't Start and Many Dead Sticks (landings).

With a 4 stroke engine you will not go wrong with a Saito or OS Surpass.

In any case I strongly suggest doing a search here on what ever brand of engine you are interested in and form your own opinion.