I can't help you a lot on the lifting part, but squats, lunges, and some basic core work and upper body exercises would be a good start. Plyos could help if you have a good plan and a coach to supervise. Take at least a week off after XC ends. Two weeks would probably be better. Your PRs indicate that you are lacking in endurance, so
after that I would do something like this:
Weeks 1-4: Easy mileage with strides 2-3 times a week, work into a lifting routine a couple times a week as well. Have one run be a decent amount longer than the others.
Weeks 5-8: Keep building mileage slowly, work in a 20-30 min tempo and some 200s at 800/mile pace, try to add in a longish run most weeks. "Long" is subjective, so base it off what you've done in the past. Keep the strides and lifting going.
Weekes 9-12: Trade the sustained tempos for some cruise intervals at a little faster pace at least every other week. Think intervals in the 800-1600m range, but don't kill yourself on these. Keep up with the strides and lifting. Mix up the 200s with some 100s/150s at a faster pace and some 300/400s a bit slower.
That was pretty broad advice, but hopefully it gives you an idea of what you should be doing. The worst thing you can do is tire yourself out before the season starts, so don't overdo it. At your level, you should get faster just by running consistently, so make sure you put in the miles. However, make sure you get in some uptempo running and don't neglect your speed. If you post more about your training history I'm sure people smarter than me could offer more detailed advice.