HI,
To maintain your centerboards, usually A Cat sailors use a rubber between th top leading edge of the centerboard and the front crossbeam. You manage the lenght of the rubber in order it is tight when centerboard is up and just a little tension when it is down.
An alternative is to glue carpet inside the centerboard's hole just below the deck, and if you can get it I personnally used some Teflon with one side with brown treatment and it can be glued by this face so I adjusted it tightly around the centerboard in order that even a little piece of sand cannot go through. It worked very well durind a few weeks and when a little piece of sand finally went throught the surface of the board got some vertical "lines".
Congratulation for your new boat.
According to my experience if you put an half degree angle (leading edge inside the boat) or around 2mm for 250 mm chord; it will improve your performance upwind.