Ask yourself why.
Do you just want to check it off your bucket list?
What are you expecting to get out of it?
Acknowledgment you're not young and if health and longevity is important to you then that will directly impact the process.
Do you have the time to commit? It's a 24/7 commitment, most all other areas of your life will take a back seat if you want to be competitive. Family, kids, work commitments or gathering, social events, special occasions etc...
It's not cheap..... Coaches cost money, more food, drugs and supplements, gym memberships, posing classes, tanning, suits, show , CPA yearly registration, show registration plus crossovers, travel costs.
These are just a few things that come to mind.
IF you're serious then do yourself a favor and the coach you decide to hire, work together for a while prior to the prep. This will give your coach much needed time to work with you and determine how you best respond. If you can't trust your coach then you shouldn't do it.
ALso, you might fit better into a class, just cause you always dreamed of being a super heavy doesn't mean you have the physique for it. Be realistic. And keep in mind, you're 40. You'll likely be up against many guys in the prime of their life.
And there is no money in the amateurs

.