Some people may try to say you're not ready, but from my past experience, I felt similar and know that I was ready but it was just a matter of me being nervous/anxioius about starting over with a new, living being. There was fear, too. I knew that I absolutely had to adopt another dog, or I would be completely miserable. I just had a lot of anxiety about making the big step. When my mom recently adopted her dog, she was nervous and anxious, but her feelings came from not being 100% sure if she was ready for the commitment and responsibility. I knew that I was, so the nerves can be caused by different reasons.
I hate to say it, but chances of the dog you are interested in being gone when you return are pretty high. I don't think shelters would accept a non-refundable deposit to hold a dog. I think they just need to get them out as quickly as possible. I lucked out when I found the dog on Petfinder that interested me, and she was with a very organized rescue group. Too bad other groups wouldn't set up paypal accounts for donations and such. It makes it much easier to do the deposit. You can ask whoever it is that has the dog you like. I found that most likely when you don't hear back from the group who posted the dog on Petfinder, that the dog is most likely already adopted. I know the groups are very busy, but it would be really nice if they would just send an e-mail or respond to voice mails to tell people the dog is no longer available. There were groups who wouldn't answer me, and there were great groups that would respond and let me know whether or not the dogs were still available. It can't hurt to ask (if you are ever able to reach them) if they would accept a deposit for a hold. If not, just start looking again as soon as you return.
When you do find "the" dog, just remember that there are going to be things they do that your other dog didn't and vice versa. I still miss some stuff that my other dog used to do, but I understand that Haley is a different dog and will not act the same or do the same things. I just accept that I can't give her bones or certain toys when people or other dogs are around (she tends to get snippy and bite around bones and certain toys). There are other adjustments I have made. It's not bothersome, because it eventually just becomes natural and you accept that you have to do it. Just as people, most dogs are going to have character flaws / quirks. You will love them anyway.
I lucked out with Haley -- I don't know if it was because the rescue group she was with fostered all of their dogs inside the houses of the group members or if Haley learned it with whoever had her before dumping her at the gates of a shelter, but she was mostly house trained when I got her. That was SO nice!!! I live by myself, am gone for about 9 - 10 hours a day for work, and didn't want to use a crate -- gave her the run of the house from day one. She went to the bathroom in the house some over the first couple of weeks, but it wasn't often. I'm not sure how I would do (stress level wise) with a dog that was completely untrained, since I don't use crate training. The dog my parents just adopted directly from a shelter has not gone to the bathroom in their house once yet, and they've had him for a couple of weeks. They take him out a lot, but still an untrained dog would go in the house some.