Requesting Evaluation of Power Plan at Rural Cabin
The bare ground + triplex is a reasonable solution, assuming we're talking type USE triplex here

Underground direct bury multiplex cables, such as the USE triplex your power company is trying to sell you on, have all their conductors (hots + neutral) insulated.  This means that you can use it along with the separate ground wire in the same trench, as per NEC 300.5(I):


  (I) Conductors of the Same Circuit All conductors of the same circuit, and where used, the grounded conductor and all equipment grounding conductors shall be installed in the same raceway or cable or shall be installed in close proximity in the same trench.


TORQUE ALL LUGS TO SPEC WITH A TORQUE WRENCH

Aluminum wire on aluminum lugs (as in a typical panel) works great -- no problems with dissimilar metals, expansion rates, or any other things that could invoke aluminum ooga-booga.  However, the setscrew-type lugs in a panelboard are sensitive to torque -- too loose is no good, obviously, but too tight can lead to problems with smashed conductors and damaged panel lugs as well, and aluminum is not as forgiving of this as copper is.

As a result (and this is a Code requirement as of 2017, see NEC 110.14(D) for details), you will need to use a torque wrench (preferably calibrated in inch-pounds, since a foot-pound unit will likely be sloppy at the relatively low torques called for on panel lugs) to torque the lugs to manufacturer specified torque in order to achieve proper reliability.  

This is especially important for you as the power company can legally sell you a type USE only triplex here (instead of tri-rated USE/RHH-2/RHW-2), and that cable can legally, as per 310.106(B), be made from the unforgiving EC-grade (AA-1350) aluminum that did such a miserable job at being building wiring back in the day.  (The assumption is that the power company knows what they're doing when terminating cables.)

Expansion is a concern here

My other concern with this setup, as amended to correct the grounding issue between the pole-panel and the house-panel, is the lack of expandability.  You'll be severely constricted in the pole-panel by the "rule of six" limiting how many breaker throws you can put in it, and actual 100A panels don't come in upwards of 24 slots or so, which limits the house panel.  Furthermore, having to replace both panels in addition to re-trenching wire and such just aggravates any potential upgrades rather needlessly, and 200A breakers take up lots of panel space.

So, going with Siemens hardware here (although equivalent parts are available in Eaton's BR line (OK) or Square-D Homeline (cough) as fallback options if you can't get the Siemens stuff from your friendly local electrical supply house), this gives us an amended plan as to the panels themselves:


Starting at the pole, we throw out the idea of using a main lug panel here altogether.  Instead, we use a convertible, 200A panel, field fitted with a 100A main breaker but factory fitted with a second pair of lugs, called feed-through lugs -- the Siemens part number for this is PW0816L1200TC, and you'll need a MBK100A kit for the field fitted main breaker.  These are normally used as service entrances to mobile/trailer homes, but provide a good slot economy in a pole-mount application like yours as well.  In the Square-D world, you're talking about a HOM816M150PFTRB fitted with a QOM2100VH main breaker instead of the stock 150A main, as there are no QO mobile home loadcenters, and putting a NQ panelboard on your pole is a mighty expensive proposition.
In the pole panel, once you have the main breaker in, the service conductors land on it, and the house feeder is taken off the feed-through lugs instead of off a breaker.  This leaves plenty of room for your GFCI (even though you won't be able to use a plug-on neutral type here, even if you go Square-D, as PoN is not available on these mobile home type panels) as well as other outdoor circuits (to other outbuildings and so forth) you wish to add later on.
Going to the house panel, you want lots of slots, and that means using a 200 or 225A panel chassis.  In the Siemens lineup, this'd be a P5470B1200CU.  If you are sticking to the Square-D catalog, you can go to 60 slots using a QO160M200PC -- Homeline has an equivalent loadcenter, but I wouldn't bother with it for your main interior panel unless you didn't have the choice.
Now that you have the house panel taken care of, your plan to run 10/2 to the shed is fine -- you might as well use 10/2 UF for the other outdoor receptacle as well, as that lets you get a straight-forward 100' of 10/2 UF instead of 75' of 10/2 and 25' of 12/2.  One problem with putting a GFCI breaker in for the shed circuit, though, is that your lights will go out if you trip it on account of a ground fault.  You'll also need a disconnecting means at the shed -- this can be a molded-case disconnect switch similar to what's used as a service disconnect for an air conditioner, though, or even a subpanel, which'd let you put a 20A GFCI breaker in for the receptacles and an ordinary 15 or 20A breaker in for the lighting, along with a main breaker to serve as the disconnecting means.