Yes. That is the exact schedule we followed. There will be many, many others travelling at the same time, so even if there is a delay, you shouldn't have a problem. For instance, there was a problem with our train, so we arrived late in Voss, but the buses were all waiting for us.
We did book our Bergen-Voss train tickets in advance. We had to do this by phone, as it's a regional train, and we were told it wasn't necessary. It probably wasn't.
You can buy your bus ticket from the driver as you board the bus. You can also buy them from the machine at the train station in Bergen, but I'm not sure how long they're good for. I made the mistake of buying mine the night before, and it was expired. So, I'd advise just buying from the driver.
I bought our ferry tickets in advance through the Visit Flam website, so I can't answer about a kiosk. We were kind of rushed getting onto the ferry because of our train and bus being late, so I didn't have time to notice things like that. My husband and I both think we remember seeing people lining up to buy tickets as they boarded, right at one of the gangplanks, but this could have been because there was such a large group of people who arrived late. I don't know.
I bought my Flamsbana tickets in advance (through Visit Flam), also, as well as the tickets for the train from Myrdal to Oslo (from the NSB website).