Outdoor Conduit for A/C and outlet
What size conduit should I use? (I was thinking 3/4")
  


Since you're pulling more than 2 wires through the conduit, you're only going to be able to fill the conduit to 40%.  Since you didn't specifically mention what type of conduit you're using, I'll list all metallic and PVC conduit.


3/4" Intermediate Metal Conduit (IMC) @40% = 0.235 in.²
3/4" Rigid Metal Conduit (RMC) @40% = 0.220 in.²
3/4" Schedule 80 PVC @40% = 0.164 in.²
3/4" Schedule 40 PVC @40% = 0.203 in.²


I'll assume you're using THHN/THWN/THWN-2 conductors, so you'll need to know the area of these conductors in the various sizes.


12 AWG = 0.0133 in.²
8 AWG = 0.0366 in.²


To figure out if the conductors will fit, you just have to add them up.

3 #8 x 0.0366 in.² = 0.1098 in²
3 #12 x 0.0133 in.² = 0.0399 in.²
0.1098 in.² + 0.0399 in.² = 0.1497 in.²

You end up with a conductor fill value of 0.1497 in.², which means you'll be able to use 3/4" conduit no matter what type you choose.

NOTES: For a look at some of the tables where these numbers came from, see this answer.


  
  Can I snake all wires for the AC and outlet in one conduit (2 conductor 1 ground for ac [8awg] / 1 conductor 1 neutral 1 ground for outlet [12awg]) - not sure the fill on this size
  


No problem, see above.


  
  When I stub up, I need to wrap around the foundation a little bit; any issue going above a hose spigot?
  


Shouldn't be a problem.


  
  Am I crazy for using rigid metal conduit? A lot of people I know say just go 'as deep as I can' and use PVC. But that's against code and even though this won't be inspected I try to stick to code as much as possible
  


You can use metallic conduit if you want, but it will likely be cheaper to use PVC (even though you'll have to dig deeper).  

I think you may be confusing PVC pipe (used for plumbing), and PVC conduit (used for electrical).  There's no problem at all with using PVC conduit, unless there's a local amendment that restricts its use.  However, you'll only have to bury metallic conduit 6" deep, whereas PVC will have to be 18" deep. So if you don't like digging, metallic conduit might be worth the extra cost.