First off this is my first post and I have been reading a bunch about this.
Then, welcome to GJ!
This would be my first real electrical adventure, but I feel pretty confident with it.
Confidence is good; but proceed with caution. You're getting into areas which are entirely new and unfamiliar to you; and based on your subsequent comments, there are still some things you need to learn about.
I have a small shed that houses all of my tools for my bikes, however it is only currently wired for 120. I really just need to rewire the entire shed as the 120 that is in it now looks like **** and was done by a hack. The shed is 150' from the meter and I am planning on running a 70a at the meter supplying a 100a subpanel. I was hoping to run 2-2-2-4 MHF in conduit at 18" down.
OK, first: Aluminum 2-2-2-4 MHF is nominally rated for up to 90 Amps; but your proposed run length will yield excessive voltage drop if you ever approach that much load current. You could use a 75-Amp breaker at the meter end to ensure that never happens; but for reasons I'll get to shortly, that might not be the best solution.
Second, at least most (all?) MHF is rated for direct burial; and I would HIGHLY recommend that you go that route. Pulling that stuff some ~150 feet through even a relatively large conduit will be no fun at all; and the expense of a sufficiently large conduit would surely be better put somewhere else. Use a large-radius "sweep" bend at each end to transition to Schedule 80 PVC for the above-ground parts.
Also, I personally would go deeper than 18 inches, regardless of "with conduit" or not. I'm not sure what the actual code requirements are in your area (it CAN vary by jurisdiction); but 24-36 inches seems like a safer bet to me. Regardless of how deep you go,
DO put in a marker tape about 12 inches ABOVE the cable.
The biggest loads I have will be 21a for my 190a welder
Welders can be a special case; but they are most typically given 50A breakers. If it is a rather small welder,
AND you are certain you'll never want a bigger one, you can probably get by with 30A.
and 15a for the 3.7hp air compressor. Im not sure if that is startup amps or running,
It's near-certainly neither. But what
IS certain is that the compressor vendor is lying through their teeth about the "3.7 HP" claim.
You need to look at the actual data plate attached to the motor which drives that compressor, and report BOTH the HP and FLA ("Full Load Amps") figures. If the notation "SPL" appears ANYWHERE, all bets are off -- the data is meaningless; see
http://www.wisedan.com/aircomp for the gory details.
All that said, if you ever want to run a REAL "3 HP" compressor in that shed, it will require AT LEAST a 25A (@ 240V) circuit; and 30A would better protect against nuisance trips on start-up.
but I have been running it on the same 30a breaker as the welder.
That is a VERY bad idea.
And given that you are going to be installing a new sub-panel in the shed, there is absolutely no reason to perpetuate that practice. Figure on individual DEDICATED 30A (minimum) circuits for the welder and the compressor.
I will also need to figure out outlets and lighting with the shop being 11.5'x20'.
For your general-purpose 120V outlets, my usual "recipe" will surely suffice: Put one double-gang box every 6-8 feet around the entire perimeter of the space, with each of the two duplexes in that box fed from a different breaker than the other one. In small shops (such as yours), two 20A circuits will normally handle the whole thing; in larger shops, split it up further as you see fit. Note that at least in anything which might be considered a "residential garage", NEC now requires that ALL 120V outlets be GFCI protected.
I am thinking 4 two light t8 fixtures overhead and possibly 2 more under cabinets over the work bench.
You're talking about two entirely different types of lighting here. Those "under cabinets over the work bench" fixtures are "Task Lighting", and don't really count toward your GENERAL illumination.
As for that, at 230 ft.^2, eight F32T8 tubes is potentially addequate; but much depends on the actual layout, vis-a-vis what you will be doing (and where) within the space.
Can I wire all of that with the standard 12-2 yellow wire you get at Lowes?
For the outlets, 12-2 is highly recommended, so that you can use 20A breakers. For the lights, 14-2 will be more than adequate, even if you put them all on the same breaker. Which brings us to...
I don't think it makes much sense to split the lights on two circuits, but am open to suggestions.
Go ahead and use two circuits for this. The reason is not the size of the load (which will be WELL under 15 Amps in any case). But rather, if/when one breaker trips (or must be thrown in order to do maintenance work), you won't be left completely in the dark.
I would hard wire the compressor with a disconnect next to it on a 30a and then two 30a on the same circuit for the welder on opposite walls.
As noted above, the compressor and the welder should NOT share a circuit.
I don't need conduit inside the walls at all if they are being insulated do I?
Insulation in the wall can actually DECREASE the current-carrying limit of a wire (as can bundling multiple cables together, and for the same reason -- HEAT). I'd have to go digging to quote the specific derating requirements; but for at least the lights and 120V outlets, I don't think it's going to be a factor.
Also, do I need to pull permits for this or would the inspector simply come out and verify everything is done correctly once finished?
That depends on your specific AHJ. But in general, if you don't pull a permit, you don't get an inspection.
).