Well the 40 acres should be plently, I would make sure you walk it before you buy it to check for sign.
As for the access, I do not know what property rights are like in the US, but in Canada our property rights are very similar, and it does not matter if you are land locked by other private owners, it is required that one right you the right of way for vehicular access.
Of course, check at your local planning department, but it really shouldnt be an issue.