
Obviously I can only go from my own experience, but I would not recommend it. I got Opi at 2 months old, when Remy was 5 months - same situation as yours, or similar, by the sound of it. He had completed a puppy training course and was coming along nicely. I wanted him to have a companion so I felt he was happier when I left him alone - and in that respect, I won't deny it has been a good thing. However, as soon as she came home, he started acting up - a lot of attention grabbing behaviour began that wasn't there before, or at the least was nowhere near as obvious. Not only that, but you'll find yourself with two puppies to train, and which need to be trained separately - dogs learn at different rates to each other, just like people, and of course the new pup wouldn't know anything that the older pup knows.
I found it not so bad in the beginning, when long walks weren't needed, but now my pups are both around 2 - and it's a hell of a lot of work. I have to walk them separately to train them (Remy pulls, Opi is very easily distracted), and do many little training sessions at home each day with each dog. Not only that, but I've had twice the teenage angst :)
The biggest problem I'm having is recall - even if I'd started training Remy for a solid recall the instant I got him home, it's unlikely I'd have had it finished before I had the second pup to train. As it is, I'm having to train this separately as well, confounding the need for individual walks. With two dogs needing two hours a day, it's a lot of work! I don't know how much exercise dachsies need, but you get the idea :)
Of course this is all just my experience - other people will undoubtedly have different experiences to me, and different viewpoints on this. But personally, I would wait until your boy has the essentials down - recall, leash walking, good manners etc - before you get another pup. I'd also wait until he's past his teenage months as well, but wait to see what others have to say. There may be someone with a wonderful multi-pup method of rearing :D