https://www.uoguide.com/ should be your go-to for questions like this. I don't mind answering but you would not have had to wait as long. Google is great as well.
You can put imbuing on any race and any template. Now to answer your questions more specifically:
Gargoyle's get a racial bonus that gives them a better chance to imbue (less chance of failing compared to other races) as well as a better chance to unravel higher end items. To answer the first thing you heard, true, best for imbuing skill.
https://www.uoguide.com/Gargoyle_Race (see master artisan under racial traits) or the bonuses section here:
https://www.uoguide.com/ImbuingImbuing augments the power of certain Mysticism spells. Mysticism does not have to be on an imbuer because it only augments some spells. Focus is to Myst like Eval is to Magery. The answer to this question is maybe. If you have room in the template, it will help but there are more beneficial skills that could go into a Mystic template than Imbuing.
https://www.uoguide.com/Imbuing (see bonuses here too)
Legendary Imbuing scrolls are fairly cheap so I would go 120 to get the best bang for your Imbuing.
I generally add imbuing to a crafter and not a Mystic. I hope this helps.