What kind of benefit will we gain by waiting another 5 months?
Many dogs have noticable changes in personality, energy level, manners and likes/dislikes once they settle in after coming from a shelter situation. One month is a fairly short time for the dog to settle in, relax, and show his "true colors", I usually tell people that 3 months is a good time frame for guesstimating when the dog is "himself"
Having done some training classes and bonding with your current dog will make that relationship strong enough to handle the chaos that comes from a second dog. The second dog (any shetler dog) will need lots of attention/time/training for the first couple months and the training of the first dog has to take a backseat unless you have nearly endless time. If the first dog has a strong bond with you and a solid basic training level, that isn't any problem but if the first dog is still newish and doesn't have a good training background, you are likely to run into behavior problems and a lot of stress trying to work with two dogs at one time.
I would suggest you contact several rescue groups that use foster homes. Offer to pay the cost of pull fees, vetting and foster care for the other dog for 2 months. Buy a crate and some food. All this will likely cost ~$300. If a rescue has a foster home available, you'd be helping them save her regardless of who adopts her later and you can express your interest in adopting her after those two months if all goes well. Maybe make an agreement that if you are the one that adopts her in 2 months that they waive the adoption fee for you (having paid the upfront costs). If you chose not to adopt her, she will at least have a significantly better chance of getting adopted having had that good start. Most rescues are very tight on both cash AND foster homes, but if you take care of 1/2 that equation, it makes it easier to find a foster (generally)
Edit to add:
No matter how well trained and calm your current dog is, you do need to expect a second dog to affect the first's training and behavior. The better he is to start with, the less the affect but it will be there. His routine will change, his amount of attention from you will change, he'll have a new playmate to pester or be pestered by, etc. My dog Chester is very solid in his temperament and not much really phases him, but he still had an adjustment period with the current foster dog and a little sliding of his training: he was more boisterous in asking for attention, began to jump on people more again after getting much better about that, getting a little more vocal because the new dog was more vocal (he's still a very quiet dog) and such. Nothing major and nothing horribly negative, just things that add some need for reinforcement training that can be hard to find time for while dealing with the second (very needy of training etc) dog.
Either way, I highly suggest a basic obedience class with your dog now and then one with any dog you get later.
