I was a boat captain with 25 years experience in Alaska and the Gulf of Mexico. There are pros and cons to flotation vest. The auto-inflates are cooler than the foam ones but aren't nearly as comfortable to wear. Any kind of flotation will be better than nothing but none of them are very good for extended use in the water.
For the Epirb
To get a signal out, you're going to need power. This means one of the bigger ones. I would never trust one of the cheap, smaller units. They just aren't going to have the range needed
What I would rather have is a good base VHF with tall antenna and a GPS. It's unlikely the boat will sink, losing power is common. This is your most likely scenario and a radio and GPS will save your life. Also, bring a couple gallons of water
If the boat sinks, which is unlikely, survival is going to be really tough without a life raft. There's something called a life float, it's smaller and cheaper but will do the job. It can also keep out the sharks.