I think you should save up money for obedience training for both dogs or see a behaviorist.
let me explain why:
My boyfriend had 2 dogs, one was a shihtzu and the other a golden/terrier mix.
The shihtzu, Dede would bully Max, because she was two years older and the house was her domain since she was there first. I didn't know my boyfriend when they got Max, but even 7 years later Dede and Max fought all the time because of jealousy/territory issues that his family never addressed.
Max became an outside dog and was constantly bullied by dede. If he got around her food she would snap, around her bed she'd go bezerk, everytime max came in the house she would run up to her toys/food/treats (she was very spoiled and also free fed) he would eat it just because he was there although it had been lying around all day in front of her.
In turn Max grew up to be a Jealous dog very effected by how Dede bullied him. He is aggressive towards other dogs and when he grew much bigger than Dede he bit her a couple times. They were in fights constantly even though the family had both of them for 9 years.
Dede passed away at 15 with cancer. About a year ago I adopted a dog (My dog not my boyfriends) who is very non aggressive and small. When I would come over I took the most extreme caution that Max wasn't anywhere near kintaro. I figured Max was initially okay with kintaro being around him so i thought it was fine, they even played together, but I never left them unattended. Then over last weekend, Max bit kintaros face because he was Jealous. it was out of the blue. Not like they got along swimmingly, but it was really without warning. I figured it was because I was feeding max lately so he grew really attached to me and bit Kintaro, after kintaro innocently sniffed his feet. Anyway after a traumatizing experience, i was really upset at my boyfriend because Kintaro almost lost his eye.
It is really a hassle having an aggressive dog not to mention dangerous to the community. I guess my point is please put both of them through training so your GSD doesn't end up aggressive. paying money now for training would prevent long term issues. And you want both dogs to be happy right? I suggest all dogs be trained/ socialized, esp big ones because they can do a lot of damage.
Your puppy may or may not be affected by how your maltese treats your GSD, but please take caution.
also as a side note, since it's already been a couple months it's too late but for future reference, sometimes if you know your dog is non aggressive but is territorial, having the dogs sniff each other out in a neutral territory (where none of the dogs own anything) may be a good idea for initial intro. Also I've read somewhere feeding is important. I only have 1 dog but I heard the dominant one should be fed 1st to prevent territorial issues? can anyone help me out there? lol
and maybe crateing the GSD around your dog might be nice, or putting a fence between them so they're introduced slowly. I think since there wasn't really an introduction your best bet would be a behaviorist.