I know a lot of breeders also use a vermiculite/soil mixture as well. How old is your beardie? Age really has more to do with it than actual size. Females should not be bred under 18 mos of age, their bodies arent ready for it. Also, was she cooled over the winter (brumation), if not, chances are you wont have a viable clutch. Since this will be her first time, dont be disappointed if you get a lot of slugs (no good eggs) it happens! About the incubator, thats really up to you. Do you only have the one female dragon? If so, you probably dont need a big incubator, and a small counter top one will do fine. Just make sure it has the appropriate temp ranges for dragon eggs (82-85 degrees). Good luck!
Melody