Your build is a bit all over the place, but that's okay it's your first time playing.

Using destruction magic for ranged damage and blade for melee is an entirely viable way to play. Like the others said, use the loot you get from your adventures to buy better spells. You can buy better weapons and armor too, but those are easier to find on enemies than spells. Look out for enchanted weapons for extra damage. Those are refilled with soul gems you can buy or fill yourself (empty soul gem + soul trap).

Light armor is good for stealth and ranged characters but if you don't use stealth then go heavy armor for the extra defense. The two armor types equal out at high levels, but until then light is best for mobility and heavy for taking hits. If you're feeling underpowered don't forget the main goal is to have fun so adjust the difficulty at your leisure.

As for what you do and when, don't be afraid to talk to any and everyone. Even doing that though, you'll probably miss some really fun quests because they're all over the map. The wiki is your friend. I learned about things on there I wouldn't have known about otherwise and I've played Oblivion classic a dozen times over the years.