May is often known for unconsolidated snow but it is popular I think because there is less exposed rock on the route then and less ice climbing. Check with the rangers, but I bet the success rate is highest in early July.
You will want a standard ice axe for most of the climb. I used a second tool only for maybe 500 feet or so out of about 5,000 feet of climbing where you want an axe for a possible self arrest in the event of a slip. At the schrund, the leader can use the two “second” tools if they need to.
I don’t think anyone uses pins on that route, and I doubt many carry a deadman. A picket can be buried “deadman style” if you need an anchor in softer snow.
Don’t know about the comparison, but the approach is done by some but probably not most parties in one day to Thumb Rock and one day back to base, but I think your 3-4 day timeframe is far more common. As I noted there is 5,000 feet of climbing on steep-ish terrain but only several hundred feet that anybody would call technical and really only a short bit that is steep (maybe a 40 foot section right out of camp, and another 75 feet at the top?).
You can certainly rent gear in Seattle - Feathered Friends or REI, I think. ‘Don’t know about closer rentals.