Posted: 08/01/2015 at 20:17
Base layers are generally lighter weight kit designed to be worn under something else as part of a 'layering' system.
Compression kit is tight fitting kit designed to improve venous return and provide compression to stabilize/minimize muscle movement.
Neither will keep you warm once it gets wet. I would suggest wearing the oldest pair of standard running tights and technical top that you own on the basis that you may need to chuck it away once you've finished.
You may also like to consider that less maybe more - depending on how cold it actually is on the day. Wet, muddy kit can get heavy and uncomfortable so wearing capri/shorts might be better. Your skin dries quicker than kit.
As for race day tips, expect to get wet and muddy and have lots of fun