hatches...........what to do?

The problems of my hatches on Arwen are keeping me awake so to speak.
Here is my problem.......

1. the plans I had for Arwen were, I think, first generation ones and showed the hatch to the forward 'under the deck' locker behind the forward bulkhead as being central on the bulkhead
2. I followed the plans because I was new to boat building........................
3. and so I didn't spot the problem..................................
4. which is that the mast is right in front of this hatch and it limits a) hatch removal - making it fiddly and b) it limits what can be put either side of the mast into the hatch size wise
5. I want to make a new 'more accessible' hatch to one side of the mast so that I can use the under the deck storage locker.......
6. ....which leaves me wondering a) how to seal up the old hatch  b) how to cut out and install a new hatch   c) whether this will weaken the bulkhead and therefore should be avoided altogether?

To add to my little woes, I have the continued dilemma of the front thwart hatches. These are two round 8" diameter inspection hatches in the vertical bulkhead that forms the front wall of the thwart. They have a tendency to leak....albeit slowly, when the boat is stored on my sloping drive and rainwater manages to permeate the tarpaulins. So I assume that in a capsize and a cockpit full of water, similar leakage through the hatches will take place whilst I am bailing out!  So............

1. can I seal these up in someway by removing the circular plastic hatches and putting ply covers over the holes and epoxying them sealed; followed by repainting?
2. could I put new better quality 8" round hatches in the seat tops so I can access the storage locker from above
3. is it worth doing all this fiddling around or should I just leave them as they are.......slow leakers and the locker space filled with 2 litre coke bottles to displace any water that may leak in?

I have managed thus far....but I was just conscious that there was a lot of stuff in Arwen's cockpit that had to be stored and tied down on our recent trip up the river Tamar; 'stuff' that could have usefully been stored away in the lockers available but that inaccessible for above mentioned reasons.............

Problems, problems, problems.....what to do?

Suggestions in a comment box deeply appreciated!