I see the benefit of the multi-wire branch circuit, but I see a lot of warnings about it and I am on the edge of my comfort zone and don't want to risk it (unless there is a volunteer out there
).
There is really no need to fear multiwire branch circuits.
There are really only two points of concern with them, one which does not apply to your shop environment at all, and another that is absolutely under your control to address if you like. The third concern is not applicable to anything remotely resembling modern wiring.
Issues:
1) They are not generally suitable for environments with switching power supplies with very poor Power Factor. Outside of a large (and likely rather old) server farm you should never see this condition -- especially in a woodworking shop! However, even in this very extreme scenario an over-sized neutral can be run to mitigate the issue... but as I said, none of this is even a concern in a shop environment. Nowadays many such power supplies include power factor correction (PFC) further reducing this issue even in server farm environments.
2) The Big Code Debate that has raged for decades over the issue has to do with the fact that code allows the two 120V circuits to be treated as two seperate circuits and thus be serviced with a pair of single-pole circuit breakers (which will each be installed onto the seperate A and B buss within your load panel). The primary concern here is that if you overload one half of the circuit and trip the breaker (and thus think the entire receptacle is dead) there remains one half of the circuit that is still live. I don't know if Code has changed their interpretation on this issue in the past few years, or not, as it is a debate that has raged for decades. However, if it concerns you, then you can simply wire your multiwire branch circuits using a single double-pole circuit breaker. That way if either side trips then both sides trip and all power in the receptacle box is disconnected and rendered safe (if, by chance, you were including a 240V receptacle in your multiwire branch circuit configuration, then the double-pole circuit breaker would be mandatory any how).
3) In *very* (very, very) old houses with multiwire branch circuits it was not uncommon for the neutral conductor to be grossly undersized which could result in overheating if the loads on each half were severely unbalanced or had very poor Power Factor. This is not an issue with any remotely modern wiring as the neutral conductor will be run with the same gauge wire as the two hots and is, thus, perfectly capable of handling a 100% imbalance outside of concern #1 (above).
I hope this clears up some of your concerns.
A few other points I meant to make:
1) Do you ever plan to install a large air compressor for pneumatic tools, venturi vacuum press, spray finishing, etc? If so then you will want another 240V receptacle wired with #8 copper so that it can accommodate anything from a small compressor running on a 20A circuit all the way up to a 40A circuit with minimal voltage drop. Locate this wherever you would envision your air compressor being located.
2) Do you plan to add A/C or electric strip heating in the future? If so then these will likely require 240V receptacles of 15A to 30A each (or a single such if both are combined into a single unit).
3) As part of your lighting circuit, if you spend a lot of time in your shop after dark then it is good insurance to go ahead and install 3 or 4 emergency lighting fixtures (they're quite cheap at the BORGs) to provide you with enough emergency light to safely power down and exit your shop in the event of a loss of power. Without such lighting it can be very easy to let your hands or arms wander into the danger zone while fumbling for the "Off" switch -- plus less chance of you tripping and hurting yourself in the dark. For a shop of any size you will need at least 3 or 4 units to get enough usable light to safely move around by and you can aim each swivel head lamp at an individual work area or aisle to boot.
