A 20A breaker is perfectly fine for #12 wire. But a single 20 circuit for a kitchen is way underpowered!
Yes, it absolutely does. You can’t afford it right now? Could you afford a fire?
I tried three times to trip the circuit with the microwave oven while the guys were here. It didn’t. They left, and I decided to warm up a slice of pizza. Sure enough, the breaker tripped. I turned off the hood light and unplugged the refrigerator. The clock on the coffee pot was on. Started the microwave oven, and it tripped again.
My old man was an Electrician, very forward thinking, and heck we had to upgrade the 15 Amp house service anyway…
As things wound up, each walls outlets had two circuits, in addition to the fridge, dishwasher and disposal. First outlet you came too was circuit A, next circuit B, third was A, etc. He also put in outlets every 3 feet over the counters. Only thing he missed was the microwave over the stove, the first range had two ovens, one down and one over the burners–home microwaves were extremely rare when we got the house.
The outlets on the front of the house were split–half were on a timer.
For Christmas lights.
I remember being astonished when they started requiring a separate circuit for the fridge.
Overnight practically every home in America needed updating. 
My fridge is still on the circuit with the kitchen wall plugs. Just like God intended in 1955. I had a circuit added for my Microwave.
I relocated the washer/dryer from the carport closet inside. I had that dedicated 220 line moved. They just went under the house and swung it around and run through the floor. It was lying on the ground. It’s stapled to the joists now.
As you have deduced, it’s the microwave. How many Watts is it rated for? 1100? or possibly 1800?
Based on a picture on this page, it’s 1,250 W. I’ve plugged it into an outlet by the door of the front bedroom for tonight, and I’ve successfully heated a 12 oz. mug of coffee. Tomorrow it will get its own dedicated outlet.
No updating required. If it was legal when installed, it stays legal. Only a few really unsafe things are required changes. Thus knob-and-tube wiring from pre-roaring 20’s is still legal.
It’s just if you start modifying that wiring that you have to bring it up to current code. That’s sometime a requirement of the local code inspectors; other times it’s a requirement of the local electricians or their insurance companies.
The kitchen is done.
Labor:
- Installed (2) outlets on the range side of the counter top on a dedicated 20 amp circuit.
- Installed (2) outlet locations on the other counter top side on a dedicated 20 amp circuit.
- Installed a dedicated 20 amp microwave outlet location on the same side as above.
- Installed an outlet location for the refrigerator.
- Removed an existing live wire from the attic due to not being connected to anything.
- Removed the existing wires feeding the outlet left of the range due to not being adequate for use in the kitchen therefore the need for an additional circuit versus the initial (2) stated.
Materials:
3 ea. Seimens 20 amp single pole arc fault breakers.
3 ea. Leviton tamper resistant gfi receptacles.
2 ea. Leviton tamper resistant receptacles and cover plates.
Misc. Wire, fixture and outlet boxes, connectors and fittings, staples, standards and wire nuts.
Total with tax: $1308.74
So over five kilobucks for the whole job. But I’m less worried about a fire.
Ability to sleep at night without marshmallows close: Priceless.
And the power strip I shortened the cord on has been removed. There are outlets on the wall now. Had I known, I could’ve saved myself $50.
You didn’t end up needing AFCI breakers just because of putting the panel in an unobtrusive spot. They’re current (2014) Code requirement for just about every single circuit in a house. About the only place they’re not required now is outside. They help prevent fires caused by bad connections at outlets heating up, power cords getting crushed under carpets, etc.
Now that you have them, you’ll find that they are also crappy old wiring detectors.
For about ten bucks more per breaker, you could have gotten combo AFCI/GFCI breakers and skipped the GFCI outlets. The tradeoff is that if you pop a GFCI, you usually know what you did and won’t do it again, so being able to just poke the outlet to reset it is nicer than having to go out to the garage to reset a breaker.