Yes you are going to get sore feet from the boots: everyone does. You will be wearing them all day for your first 6 weeks (or so). Everyone drips about their feet right up until ABLE, but not many cadets have really bad issues. Thousands of successful cadets have got through training without buying boots before arriving at BRNC. There is nothing more a cadet likes to do than drip (other than offer chad advice) to other cadets, mates and just about anyone who will listen. There is, in my mind at least, very little point in buying your own boots. Lots of reasons for this:
The training is pretty tame during the first few weeks to account for the boots;
You may buy the wrong type;
If you can't man up and deal with them is the Navy the right job for you; and so on...
(You will not be able to draw anything out of stores until you join, that I am certain about!)