There are a number of wear parts on a bike that may or may not need replacement, including chain, brake pads, cables, cable housing, bearings (wheels, bottom bracket, headset) and your tires. You can just replace them all in one clump (I guess I'd want to know what an "Overhaul" consistes of) or perhaps depending on the type of weather you train in do it partly now, then finish it closer to the race season. For now, why not have the headset lubed, check wheel bearings and bottom bracket play, check chain and replace if needed to replace any frayed cables and worn brake shoes. If the bike is sticky in shifting or braking, perhaps new cable housing also. Also, ask then the remove the seatpost and lubricate so it doesn't get stuck in the seat tube. How's that sound? I generally will replace some at a time over the season but never have the time to do a complete job.