Hey Brian,
I’ve had success holding a big kettle bell in each hand for my strength work. Up to 40-50 lbs each seems to be about the limit of my grip strength at the moment, but that has been enough for my work. Then you can always adjust the weight of your vest or backpack to increase or fine-tune.
As far as when to incorporate hill sprints, I’ve actually found it helpful to do them in the same week as my max strength, so each workout is done once per week, with an easy day separating each. This keeps my legs firing and feels like I’m always translating that strength into my sprinting mechanics. Mixing in a few strides into my easy runs when I feel fresh seems to help as well. Then once I feel like I’ve built up enough strength, those max strength workouts get replaced by ME workouts, while the hill sprints stay. Curious how others approach this though.
Good luck,
N