Getting a new dog

hi all,
I'm about to rehome a dog from a family that can't look after him anymore and I was wondering if anyone had any advice on settling him in with my current dog?

I think I would opt for a meeting (on neutral ground, like a park) before committing.

If this is not possible then I usually settle my fosters in by starting off with a long walk (or two). Tired dogs are usually happy dogs and walking is a good bonding exercise.

We went for a walk with him this afternoon before deciding to have him. They both seemed fine.
At home they are both very excited/stressed and although they want to play together the new dog (who is entire) keeps humping Loki, and pushing Loki into a submissive, tummy in the air position.
They neither of them seem to want to calm down at all and at the moment I have Loki upstairs with me and my son has Charlie (the new dog) downstairs.
Any idea how to get them to settle together??? The humping is really a bit much and Loki doesn't like it at all