If I feed regularly, can I walk out in sunlight without causing a panic? is vampirism recommended for a battle-mage playstyle? Any other advice you all have would be nice, thanks.

If you feed once a day, you will remain at stage 1, so no hugh effect will take place. When you reach stage 3 people will refuse to talk to you, and at stage 4 people will kill you on sight.
In the sunlight you wont regenerate Health, Stamina or Magicka, so carry a lot of potions/enchanted gear
They also get a lot of magic buffs, so a battle mage suits them perfectly.
Its a different kind of playstyle, which can become frustraiting early on, but can eventually make you quite powerful.

so stage 2 is the highest I can go & still be able to shop at stores?

make sure u get necromage perk from the restoration tree it will make your spells & enchantments alot more effective...