To questions (minor chords and pentatonic scales)

Two questions that I remain having trouble to get answered are:
1. Is the minor key simply the I IV V but in minor for instead of major

I am not sure if I understand the question. The primary chords for natural minor are i - iv - v (or Im - IVm - Vm, as some prefer to notate this.) In Am it will be Am - Dm - Em.

But in harmonic minor and melodic minor the chords are i - iv - V7, which in Am will be Am - Dm - E7.

I suggest that you go to
http://www.torvund.net/guitar/Theory/24-Minor_harmony.asp and the pages
that follows on natural minor, harmonic minor and meldoic minor.

Q2. Is on when to use the different scales. Are minor pentatonic scales only used with minor keys or can they be used with major keys where the minor pentatonic scale is the same as the relative minor in the major key? For example, the A Minor pentatonic scale can be used in the A Minor Key AND the C Major Key (because the relative minor to C Major is A Minor). Could
it be used anywhere else?

You will often use minor pentatonic scales over blues progressions with majort chords, and if you are using power chords.

If you think of playing A-minor pentatonic over C-major, you will probably end up with C-major pentatonic. They share the same notes.

I have also sent this answer to my comments and questions blog at http://olavsguitarq.blogspot.com/