I am hesitant to reply here as I am no expert but am in a similar situation to yours. Multiple blisters, many between an epoxy barrier coat and several thru to the gelkote.
To others reading this if I am off base in my comments please correct me.
The blisters between the barrier coat and the gelkote are a non issue in that they are not penetrating the hull. 3 approaches can be taken with these, assuming you are doing the work your self.
1) Pop the blister, allow the water to drain and leave be.
2) Pop the blister sand around it and fill with epoxy putty
3) Remove the barrier coat completely, dry the boat and reapply.
I have chosen #2 Why? The reading I have done suggests these blisters are not a problem(yet) as they are there thru osmosis only and have not penetrated the gelkote.
The real problem starts when you have hydrolysis. This occurs when the blisters are not removed, the water penetrates the gelkote and chemically reacts to the polyester resin, breaking it down.
Basically these blisters are just water sitting between the two layers and if removed as they appear they should not be of major concern. If your situation is like mine it will be an on going job in that my epoxy barrier coat is slowly separating from the gelkote allowing the water to "pool". The proper approach would be to remove the epoxy barrier coat completely but that will have to wait. For now removing and filling each blister as they appear will prevent any real damage to the hull.
The blisters that have penetrated the gelkote.
As mentioned above this can become more of a problem because if left to sit hydrolysis can set in.
I have several of these, I have concluded that hydrolysis has started because when the blisters are popped red fluid comes out.
For these blisters I have sanded aggressively around the blister and when required removed a layer of cloth from the hull. Basically sand down deep and wide enough to removed the damaged area. They have been left to dry and will be filled next spring. It is important to note that all of the infected areas must be removed, if not you make the situation worse when applying the epoxy putty, trapping fluid into the a section of the hull where hydrolysis has already began.
It is worth noting that hydrolysis takes time to set in, which is why popping blisters to remove the water helps to prevent any or further damage. If blisters in the epoxy barrier coat or into the hull are flushed on a regular basis they are for the most part more of a cosmetic problem than a structural one.
As to doing the work yourself verses paying, only you can say which is the best route. For me, I do the work myself. It is not hard and requires a min amount of tools. A good orbiting sander with a vacuum attachment. A shop vac and plenty of sand paper. West system has all of the documentation you need on their website and all that is left is time and a boat yard that will allow you to do the work.
Again I am no expert so if I have written in error I hope someone will correct me.