I just got back from Veneto, and here is my experience:

I bought my tickets either in the railway station at the counter or by machine (with help of rail employee), or paid a little extra from local travel agency.

All my tickets are open tickets, 2nd class, which means you can take either "R" or "RV" train. It worked fine for me. From Venice to Verona only takes 1h27min on "RV" train, cost only euro 8.05.

Since it is open ticket, make sure to validate before boarding, otherwise it is hefty fine, saw it happen to a couple foreign traveler.

My experience is to buy when you are there, no need to plan it ahead.

We spent 17 days in the Veneto region, and didn't encounter any strikes.