Re: newbe question about freshwater tanks
If the boat requires new bulkheads then there is a fair investment and work effort before you can even sail it. Not having a good interior will make it harder to sell when you out grow it. Those are good reasons to look for a better boat.
"Free" boats rarely seem to be really free. I think most are probably more expensive than decently cared for but simple $5000 boats.
boats that I sail on regularly: Pearson 28-2, Rondar 505, Yankee 30, Blanchard Junior