i thought the commander had to be a legendary creature

This is a Pauper EDH deck, as states in the description; it uses an uncommon commander and 99 common cards

Frogmite or Myr Enforcer? Free artifacts seem great with this General.

They are great, but white has a lot of problems generating card advantage. Frogmite is a 2/2 which basically makes it's only ability to chump block. I'll try out the Myr Enforcer; having a 4/4 base with some equipment seems pretty good, and it'll be close to or free to play.

Isn't Oblivion Ring uncommon?

I'm by far no expert, but 25 land in a 100 card deck is way too few, no? We want at least 32 if not 34 or even 36?

I run so few because the average CMC is 2. In order for the deck to function I need three or four 1-2 CMC artifacts in my opening hand and two lands. It's built similar to a white weenie deck that only needs 3-4 mana on the field to work well, but with cheap artifacts instead of cheap creatures. Having to pay the one extra mana for my artifacts to generate a myr also slows down the speed at which I can play spells, so I'm able to draw more cards before I play out my hand.

Also, Oblivion Ring was printed at common.