A lot of what Bob said but I'll add...
Racing is racing. Same thing as in a fight if you approach it laid back you often get your clock cleaned, quite simple. Except in a bike race you just get dropped, not a blood spot on your eye that takes 3 weeks to dissipate. The worst culprit is usually pride. Good news, If you don't approach your training "laid back" you can probably have fun during your first race instead of just hanging on for dear life, it sounds like that won't be a problem.
Not sure what country you are in (US, Germany?) but I remember lining up at the first Cat5 race of the season in Central Park after a decade off the bike. The kid next to me was wearing knickers and I playfully said "nice tan". He replied yeah me an my team just got back from a Florida training camp. Wait! Wut did he just say? When I raced in the 80's, most of the guys lining up at the start of entry level/citizens races had bellies and hairy legs, now that was laid back. This kid had a team, deep section wheels, and an even deeper tan from a FLA training camp! WTF! Am I lining up with the 5's or the 3's?
Depending on where you live, the entry level scene will have varying levels of talent. And in the bigger pools there's often that guy, aka the sandbagger, who's been lining up with the 5's for the last 3 seasons who the race marshall's haven't quite caught onto yet and who should be a Cat3 based on his speed.
The good thing is a number of entry level guys don't understand the importance of actually riding a bike to be fast on the bike as they are too busy arguing about the importance of doing squats are on the forums. Don't get me wrong I love squats, they just don't seem to make me any faster. As Bob said some of those guys possess ungodly power combined with atrocious bike handling. Do not, I repeat do not follow those wheels. The good news is entry level circuit race distances are usually quite short - my local park Cat5 races are 17mi, compared with the 35mi the 4's race. Cat5 RR distances however are usually on par with the 4's, 60 miles give or take and this is where many starting 5's who have followed the "time crunch" plans without the appropriate miles in their legs tend to suffer.
In preparation for the 5's with it's combo of comparatively short distances and shortage of race tactics, regular rides with one or two longer rides each week (2-3+ hours), and a half dozen or so full tilt efforts lasting 2-3 minutes sprinkled throughout for a few months are a good start.
Unfortunately many of the plans geared toward folks on limited time seem to jump into intervals right away. They are actually in direct contradiction with your goal of "building base". Best way to build base for a beginner cyclist (some but not all fitness from other activities is transferable) imo? Ride 4 or 5 days a week consistently, mostly at moderate speeds, adding distance over time, and with groups who will help stretch your legs but groups which don't have you busting a lung for the entire ride. Try not too take more than one day off between rides unless you are sick, run down, or just feeling mentally drained, but some rest beyond a good night sleep after hard rides is definitely required to get stronger. Base is all about consistency, frequency, and moderation.
Now for your original question:
Cyclists Training Bible by Joe Friel and The Ultimate Ride by Chris Carmichael are a couple I recommend. If you have the time go to a well stocked Barnes&Noble and browse, there are probably quite a few titles you may miss by going solely on the advice of the peanut gallery.