Hi everyone.
I'm a DIY newb and I need your help. I recently purchased some 3/4 solid oak to lay in my livingroom. I pulled up a corner of the carpet to see what kind of underlayment I had and noticed that there was 5/8 inch thick plywood under there.

I let the wood sit in the living room for two weeks, purcahsed a Wagner moister meter, and confirmed that the underlayment and oak boards were within 4% of each other. Last weekend I began pulling up the carpet and noticed that my underlayment is particleboard.

Only one sheet of plywood was installed (perhaps after the original construction) in the very corner that I pulled the carpet to check.
I also noticed that my subfloor is only 1/2 inch thick plywood.

I purcahsed 1/2 inch plywood sheets to replace the underlayment. Will the 1/2 inch subfloor and the 1/2 inch underlayment be enough?

Also I noticed two problem areas on the subfloor. In one area there is a small hole formed when some idiot layed a peice of wood to cut flat down on the subfloor and then cut through both leaving the need for a 6x16 inch patch. For this I plan to nail 2x4s to the joists to support a small patch cut from 1/2 inch plywood. Sound OK?

The second area is a wet spot in a corner that appears to be from my wife's sloppy plant watering. The wood is soft and moldy. Here I plan to cut as close as possible to the wall removing a 24x24 inch square, install 2x4s to the joists and cut small sections of joist to attach to the sill plate for supports and cut a new peice of 1/2 inch plywood to patch the spot. Is this acceptable?

Thanks in advanvce for your help and advice.

Anyone?

I missed this post before. The 1/2" plywood underlayment is enough. Your plan looks fine to me. Good luck.