Help! Advice for Rescue JRT puppy

I have never owned a JRT and know very little about their breed except what I’ve read online. A 6 week old (vet estimated) puppy turned up on my friends doorstep, and it needs a home. She appears to be shaky and small, and slept all the way through her first night. Appears to be dumped. Vet has no health concerns and said other than being a little skinny and hungry she seems fine.

I have an 11 year old lazy chihuahua male. He doesn’t have any interest in playing with toys and prefers to chew on a bone or sleep in your lap. He spends long periods of time home alone and he sleeps in our bed. He is very happy with his lifestyle. He doesn’t even run away and stays near without a leash. He roams the backyard freely which has holes to other yards with bigger dogs. He barks at them occasionally but has never tried to escape into another yard and is potty trained.

Around other dogs he is nonchalant. He has cousins that he ignores and prefers female dogs to male ones as he can be a little aggressive towards males. He will probably not cuddle with her or play, but I have almost no doubt he will be fine and just ignore her most of the time. He has never even snapped at one of the girls even when they were puppies.

At the moment, we have someone who will always be home with her except maybe if we leave for a few hours somewhere she can’t go like the movies or to dinner. In a few weeks to a month, she will probably need to be on her own 8 hours a day while we are at work. I’ll separate them until we can trust her to also have free rein of the house like the chi.

What do I need to do to make this transition smooth? What do I need to expect with her? Should I be letting her sleep with us, or crate train her (he is not now and will never been crate trained)? Is she going to be too high energy for us?