I am going to try my first gluten free cake tomorrow and I was wondering if I can just substitute coconut flour for regular flour or if I need to add anything like xanthan gum.  And do you know what ratio I need to add?  Is it a certain amount per cup of flour?   I would like to use my regular coconut cake recipe with the coconut flour.  One recipe said to use a cup and a half of almond flour and 2 tbsp of coconut flour and I wasn't sure why not just all coconut flour?  Any help will be much appreciated!!

I don't bake gluten free because of the cross-contamination, so I have no advice on flours. I just wanted to warn you that if you bake with regular wheat flour there will be residual flour on your mixer and in the air in your house, so be careful with the gluten-free cakes for people with serious reasons for going gluten-free. It's one thing to bake an alternate recipe for someone who's doing gluten-free for a fad, but if it's for health reasons you can make someone really sick with even a little bit of cross-contamination. Wiping your equipment down well before baking isn't enough for a lot of people. I have a friend whose kids are so gluten-intolerant they end up in the hospital if they eat anything with gluten in it, so be careful!

It is for a friend who is gluten intolerant but she already knows I bake and said that's fine but thanks for your concern!  I really just need the baking advise.  If anyone can help, I could really use it!

Hi, I think you already baked your cake 
to answer your questions:
NO you can not swab wheat flour for any gluten free flour , esp the coconut flour
coconut flour absorb a lot of fluids and usually recipes made with coconut flour calls for a lot of eggs like 5 eggs for 1/4 cup of cc flour
 
RE- One recipe said to use a cup and a half of almond flour and 2 tbsp of coconut flour and I wasn't sure why not just all coconut flour? 

You can not do it for the same above reason, you will need to adjust the liquid ratio 
if you dont have almond flour you can use grind almond instead 
HTH