More specific questions might help...your request is pretty broad.

Breton is a great race for magic. Magblades are tons of fun. So it should be a good character. And yes, you will be able to cloak forever and ever.

I’d level both light and heavy armor. You will probably wear mostly light, but you may wear a piece or two of heavy. So you can level it and invest in the first three passives in heavy.

There are plenty of skill points in the game to unlock and play with any ability in your trees. Feel free to try all class abilities that have a magic morph (which is almost all of them). All of the destro staff abilities. You can level resto, but you don’t need many of those abilities.

Another tip is to work your legerdemain up to at least level 16. Then you can spend four points to reduce sneaky costs by up to 40%. This is very helpful on a mag blade and will be essential if you PvP. My grind is to spend one point to increase fence transactions. Then empty the inventory and go to the ships in daggerfall...there are few npcs. Steal everything, and fence it all. It’ll take ten or so days to get to sixteen. Leveling legerdemain also increases the quality of stuff you steal and raid, so that’s another perk.