Goldendoodles are great in the fact that most do not shed or have very little shedding, but with that comes more maintenance in grooming. Keeping a Goldendoodles coat brushed out is important for the Goldendoodles health and for your groomer to have an easier time grooming them, which will allow you to keep your Goldendoodle in a longer coat.
I recommend getting a comb for daily (or a few times a week) brushing. These combs will go right down to the skin, so that the mats are brushed out. It is important to use these combs regularily to avoid mats and your groomer will love you (As will your Goldendoodle).
I also recommend getting a slicker brush. If you want the traditional Goldendoodle look, this is the easiest way to get it. It will fluff up your dog and does maintain the outside of the coat very well. The only thing this brush does not do in get the undercoat (where the mats are) at the skin, so we always recommend use of the comb with this brush.
There are many other good brushed out there, but you only needed to pick two, these are the two that I would get.
As far as, how often your dog should see their groomer. This will depend on what type of coat that your Goldendoodle has and also will depend on how long you want to maintain your Goldendoodles coat. The curlier the coat the more grooming requirements, but also the less shedding. If you want to keep your Goldendoodle in a long coat year round, you will probably require going to the groomer every 6 weeks. If you are willing to shave your Goldendoodle down a couple times a year and they have a wavy instead of curly coat, you will probably only require going to the groomer 3-4 times a year. We often shave our Goldendoodles down in the spring/Summer as we are active outside a lot in the country, so the dogs often get into burrs and lots of mud, so this is just an easy solution for their and our convienence.
Another big aspect of maintenance of a Goldendoodle is cleaning out their ears. It is important because these are floppy eared dogs and because of the poodle, they do grow a lot of hair in their ears. You NEED to pluck the hair out of their ears. They will continue to grow lots of hair in their ears and eventually there will be no air movement and they will get ear infections. Ear infections can cause a number of issues in dogs, but are easy to treat and keep on top of. It is important to note that dogs do not have nerve endings in their ears, so you are able to pluck the hair out of their ears without hurting them. You can just stick you fingers in their ears, grab ahold of the hairs and pull them out. The puppy might whine a little, but it is more awkward that actually hurting them. You can buy powder at any pet store that will help with gripping the ear hairs as well. But, for harder to get hairs in the ears you can get hemostats. They will easily hold the hair, so that you can pull it out. Just be very careful with these as you only want to grap hair and not any soft tissue in the ear.
Majority of groomers will automatically pull all the hair out of your Goldendoodles ears, but if they don't always ask for this to be done.