First cyclocross race - how to choose and set up the bike I have never raced but there is a cyclocross race at a park near me next weekend.  

All it said is some sand and some drop offs.

I would like some advice on selecting a bike and setting it up.  

I have Bianchi Cylcocross Concept and Salsa La Cruz Ti. 
They are both Ultegra and greared the same 48/39  12-28. 
Both cantilever and weigh about the same.
The concept is my workout bike and the Salsa by daily banger / commuter. 

The Concept feels faster but the Salsa feels more stable.
I also feel like the Salsa can take a crash better. 
So my thought is the Salsa.  

I take it they race with cleats? 
For a first race should I cleat. 
I am comfortable with cleats. 

I have touring tires on them now but I have some Conti 32 Twister. 
Would they be OK? 
Would I run them at max pressure? 
I weigh 165.

I also have a Niner Air 9 Carbon single speed mountain bike with carbon fork, disc brakes, and tubeless.
I am not comfortable on big drop off on my cyclcross. 

I rode the park on four set ups.

With 32 mm it was just too fast for me. 
There are some downhills with rocks that I would need to run at max pressure and even not in a group picking my line I was not comfortable. 

The Air 9 was super stable but not very fast. 
I rode the park 15 minutes each direction and if the long hill is uphill then the single speed is not geared correctly but I am pretty sure they will have us ride down that hill.   

The Salsa with 38 mm small block at mid pressure felt stable but still has a speed. 

As far as cleats.  I would not want to ride the downhills without em.  Getting bounced hard enough that need bike attached.
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.