I don't really feel qualified to give you advice about painting your Latex mask.  There are lots of folks out there with more knowledge and experience than me.  Your personal artistic ability and macabre predisposition are your best guides.  For what it's worth, here's what I learned during the last phase of my mask project...
     

My first mask painting session was also my first time ever using an air brush.  If you have the chance to learn how to use one of these things then do it.  I quickly discovered this is not something you can just pick up.  There is subtlety and finesse that I expect will take a great deal of time to master.  Nevertheless, you can at least apply a base coat with one and do the detail work by hand.

I used plain old Testor model paints.  By the way, did I mention that you really shouldn't try to wear this thing?  These masks will end up on the north end of some props, but I wouldn't want one stuck to my face.

I started with a nice base coat of thinned paint.  Mix a drop of paint to about 3 tablespoons of thinner.  Think white-wash.  If you don't have an airbrush to mess around with, use a small brush or sponge and dab the paint on in patches.  It's okay if the coloring looks uneven.  This guy's supposed to be dead, after all.

When you have your base coat down, repeat the process using different shades of brown or green.  If you keep the paint very thin you can go back over the same area several times to shade certain areas.

Use flat paints unless you don't mind your monster having a shiny face.  Use high-gloss un-thinned red and brown to highlight features such as bloody scars and cuts.  Casting imperfections can be turned into puss-filled sores.  Use unusual colors like green and yellow thinned down and dabbed all over to cast an unhealthy glow on your monster's face.  If you want to cover more surface in a shorter time use a sponge.  Just keep the paint thinned way down and have fun.

By changing colors and using different techniques (sponges versus brushes) from mask to mask you can come up with some really neat and different results.  The last two pics on the right are of a second mask painted with different colors.  When choosing colors to paint your ghoul, keep in mind where he'll be stationed in your haunt.  If it's going to be really dark then he may not need much of a paint job at all.  In fact, you could just mist the face with luminous paint and sit him in front of a black light.

Don't sweat it if you don't like the direction your paint job is going.  Just paint over it.  Keep your paint thin and use different tools like paper towels or Q-tips.  You don't *have* to be proficient with an airbrush to achieve really good results.  Just use your imagination and be patient.