I really do not care which temple (or even Dark Brotherhood) is the fastest to be able t o buy potions, but I need them! Suggestions? I read the DB allows you to make tem at Rank 3, but there may be Temples that allow you to buy at rank 2?

Also, are there any artifacts that restore magicka?

1) A lot of your questions can be answered by starting here: http://www.uesp.net/wiki/Daggerfall:Daggerfall

2) No, but there are 'Cheats" available.

Many temples allow you to buy potions at low rank. But even then it's just luck of the draw as to whether they'll have any Restore Power potions on hand. Personally, I find potions to be very impractical in Daggerfall--they aren't as ubiquitous as they are later in the series.

As for replenishing magicka in general, remember that the higher your willpower, the faster your magicka restores while you rest.

I've found a little trick (i. e. "small cheat") when buying potions.

I don't consider that a cheat at all; more like a senseless annoyance the player has to put up with. I don't see why they couldn't make potions stack and give you the option to select how many you want to buy, like they did in Arena.

same goes for the Soul Gem MErchant of Arkay Temple, just leave and start again, till you find Dragonling Soulgem!