First cyclocross race - how to choose and set up the bike
Most cyclocross tires are 33-35mm and with tubulars (glued to the rim) many will run very low pressures (20-22 psi). I run 35mm clinchers and get to each race early to pre-ride a lap or two to dial in my pressure, typically will run 28-34 psi depending on how rocky the course is, I don't want to pinch flat, but really like the lower pressure as each lap it typically gets more and more muddy and you want the grip, especially on the off camber sections.

Cleats or no cleats is going to be more about your comfort getting in and out as you will get on/off the bike to carry up stairs/run-ups, through sand pits and barriers. This is about speed getting unclicked and clicked back in and right up to speed. Search on You Tube for cyclocross mounting.

You did not mention disc brakes, but with rim brakes, the sand will mix with the mud and wear your brake surface. If short and fast I'll ride the sand pits, if running I carry my bike, so go with the lighter bike.

Many courses have run-ups and barriers to carry your bike, so go with the lighter bike.

Many races have a 'pit' area for you to leave extra wheels, or even a different bike, so bring both bikes, get there early take a lap on each and race the one you like better. Put the other bike in the pits and switch if you get a mechanical or pinch flat. If this happens far away from the pits, you must run the course with your broken bike - you cannot leave course and take a shortcut, fix or switch and then get back on course.