I say go all 9spd.

13 years of using 9 spd and I've never had a problem. If they are "weaker" than 8spd, I'm just lucky? I can set either up to shift just fine.

But, if your not willing to properly upgrade everything, just find shifters and v-brake compatible brake levers and stick with 7 spd. I moved away from 7spd in 2001 and will never go back