awww i'm soo sorry brutus seems to be having so many problems. Allergies aren't as bad as your vet made them seem. You can keep them under control with shampoos, or topical creams. Or you can take medication for them, like benadryl or hydroxyzine (Rx).
As for the k-9's did she say why she thought just the k-9s needed to be pulled? Does he have a slight red line right above the tooth line and is it only by the canines or does it o above every tooth? this would be gingevitis or perialdontis disease which can be fixed with a cleaning. However $500 for a dental in NJ is ridiculous. Where do you live in jersey? the vet i go to doesn't charge that much for just a cleaning.
And the LPs, you can start him on joint protection now like missing link plus to try to prevent them from getting any worse. i know Jodie (luvmysissy) has sissy on this for LPs. Since Brutus only has a slight problem now you can do things to make sure it doesn't get worse fast. not letting him jump up or do stairs could help. However he will probably eventually have to have knee surgery.
Brutus is still an overall healthy dog. allergies, dentals, and knee problems are all common and can happen to any dog really. it just stinks that you were hit with all three at the same time.