Does a Long-Uninhabited Tank Need to "Re-cycle?"

With your plants and pond snails, along with decomposing plant matter, you would have likely maintained some level of a bb colony, but that would be limited to the extent of ammonia/nitrites being produced to sustain it.
RCs will not produce an immediate, large bio-load that the bb will need much time to adjust to, so I simply suggest you add them in a reasonable low quantity to begin with, adding more as time goes on, in the event you were thinking of tossing in a large number right from the get-go.

I agree with Paul, shrimp are not going to make that large of an impact on the bio-load.

If you want to trade off you could remove as many snails as you can catch. Without them contributing waste you could get an equivalent bioload of shrimp. Plus, the plants ramp up pretty fast when there is a new source of nitrogen for them.

I think your tank will be just fine.

If you were thinking of a larger bioload, then I would start the fishless cycle, but use fish food as the source of nitrogen. Snails will eat it, and bacteria will grow.