Well it's been since Saturday afternoon that my girlfriend and I have had Jaco in our care. It's been exhausting but nothing unexpected and an almost entirely positive experience thus far. Again, thank you all for the comments and advice thus far, it's been very insightful!
Juniper, our 16 month old female, and Jaco, the now 14 week old male, have REALLY taken a liking to each other with no violently aggressive behavior at all. Juniper's behavior and personality have remained stable…we were worried about a lapse in some of her training especially potty training. That has made much of this transition so much easier. She's also still half-pup so she's really tolerating Jaco well. Pat (tanza) called it, to be dominant and at twice Jaco's weight Juniper pins him to the ground with her jaws around his neck until he squeal or even shrieks. But he challenges her at absolutely every opportunity he has! He was very skinny when we got him, the rescuer wasn't sure why because she fed him right and but only had him a week...so he's very, very food motivated and very velcro dog around the kitchen. But he also will just take whatever Juniper is chewing on at the moment simply because she has it and not him. And Juniper will let him take it but a minute later will crash in on him for the pin routine to show him who's really boss but on her own schedule oddly enough, passive aggressive really.
But I'm kind of worried how pushy he is at such a young age. If he's this competitive with Juniper at this age, will it only become worse? Could it eventually lead to violent aggression (over food, for example)? He has even humped Juniper half a dozen times...at 14 weeks old!? What's up with that? Should we be worried he's going to turn into "one of those dogs", not to mention a dominant, potentially violent prone dog (with Juniper and/or stranger dogs)? We worried about Juniper being too aggressive in her play when we first went to the dog park but 90% of dogs absolutely love her or tolerate her just fine despite her high level of activity and play-aggression (biting at neck, pawing at the body, etc.)...so I feel like we lucked out with her, but it's likely we won't have that same luck again especially with a male, am I right?
Besides those little worries about his behavior, we are absolutely thrilled about bringing Jaco into our home! We're just anticipating potential issues in the future regarding socialization especially for playing at the dog park...but should we? And should we anticipate dominance issues between Juniper and him given the indications this early on? I know males and females will tend to not be aggressive towards one another but with how dominant and aggressive June is (when it comes to playing, not being violent), I fear they could get into a pissing match when he reaches full size and strength. This is all just speculation at a very young age for Jaco BUT no matter how many times Juniper makes him shriek he keeps coming back for more...and I have a feeling that sort of behavior from him isn't going anywhere.
Thanks again for continuing to provide me feedback, everyone's experience is greatly appreciated!