I have a vet, very familiar with small animals, so age has not been that much of a concern for me, nor has weight. My concern is the worry, which is always there, no matter the weight or age. Not to mention the cost of a second procedure within a few months.
My Samantha had like 13 baby teeth removed during spay. Most were just "picked" out, but several seemed to be stuck between the adult teeth, and gums.
This must be taken care of. So I would wait, and save the second trip, money, and worry.
As a side note, most of mine have humped on occasion. Some more than others. All spayed/neutered.
Another side note, I take my healthy males in for neuter on a Friday, and keep a close eye on them over the weekend. With females, I take an extra day off. They do amazingly well. I wouldn't worry about waiting. I don't believe it's necessary to take a week off.
Oh, and LBB was neutered at 5-months of age. Yep, he lifts his leg, along with many shelter males, I've fostered, who were neutered by 4-months. I do not believe early neuter has much to do with that either.