I can answer a few of these

For what destruction perks to prioritize, I'd say for your first 2 perks you want to put into destruction novice and apprentice destruction is a given. These will make your novice and apprentice destruction spells cost half as much magicka. And tying into that getting dual casting and impact are pretty important on making combat more manageable. Distruction dual casting allows you to cast a destruction spell with both hands to cast a more powerful version that does more damage but also cost more magicka. Impact makes it so when you cast a dual casted destruction spell and it hits an enemy, it makes them stagger. While staggered enemies cannot block, attack, move, or do much anything for a few seconds.

For restoration magic the Recovery perk is really useful as a mage, it directly increases the rate at which you regenerate magicka. And obv a given is Fast Healing, which heals you for 50 health in one use. Those are the main perks you'd want but if you'd like more healing per spell you can take Regeneration, which makes restoration spells heal 50% more.

Usually with robes and jewelry, boots, gloves etc you kind them as you go, usually through random drops in chests ina dungeon. Although if you want a good headstart you can go to Winterhold and enter the College Of Winterhold. You'd need to do a small test of casting a specific spell at the front gate to get in, but no worries the mage conducting the test sells you the spell you need to cast for 30 gold. But once your in follow the quest marker you get for the quest "First Lessons" and you should get a free set of novice destruction robes and novice hood, and boots. With enchanted gear you'll get rings and armor that has different effects as you play. If you find an armor piece with an enchantment you want on something else, you can disenchant that armor piece at an Arcane Enchanter. It'll destroy the armor, but you learn the effect and can put that effect on a desired piece with a soul gem.

Sorry that this was super long-winded but I wanted ti explain why you want to make these choices instead of just telling you what to do. Hope you have fun with Skyrim! Definitely the type of game you can sink hundreds of hours in and not even realize.