This is actually very close to how I envisioned my character to be. A heavy armour wearing, mace weilding magic-user. My plan was more to have the summoned creature do all the dirty work rather than basically being bait, and I was torn on the armour as well when I read somewhere that wearing armour had a negative affect on spellcasting. Is that a genuine concern with this type of character, or is it more for mages whos focus is more on destruction/restoration?
Any advice on what other kind of majors/minors would be most beneficial for a character like this? Mostly just curious, as I'll probably just go with whatever I think will be used most.
There is a penalty to the magnitude of your spells if you are wearing armor. Or if it is the kind of spell with no magnitude (like a summons), it reduces the duration. The amount of penalty depends on your Heavy/Light Armor skill. The higher your skill, the less the penalty. Even with a low skill, it is not that much though. http://www.uesp.net/wiki/Oblivion:Magic_Overview#Using_Armor
As far as major/minors Oblivion is very counter-intuitive when it comes to picking those. If all seven of your majors are skills you use all the time you will level up too quickly, getting only small attribute gains when you do. The monsters are scaled to your level, but they will be getting bigger bonuses. So the game actually gets harder because you level. There are several ways around it. I find the simplest is to take 3 skills I will regularly use as my majors, 3 I will never use, and the final 1 a skill I will only rarely use. Also make sure not to take two or more skills that are based off the same attribute as majors (like conjuration and alchemy). That also insures low bonuses at level up. Just have one major skill you will use per attribute.
Some skills to always keep away from as majors are aforementioned conjuration and alchemy. Both level up extremely fast. Especially alchemy.
On the skeleton, its power does not scale with you. It always has the same stats. So as you go up in levels, you will want to replace your summon spell for something more powerful. There are several different types of skeleton, that become progressively more powerful, the regular Skeleton, Skeleton Guardian, Skeleton Hero, and finally Skeleton Champion. You can find a list of all the conjuration spells http://www.uesp.net/wiki/Oblivion:Spells#Conjuration, along with the skill level and magicka you need to summon them.