Amplifiers for vocals..........

The clarity depends more on acoustics than anything. Even if you get the best sounding amp, your vocalist would still sound muddy over the mix if you practice in a garage conditions. The only decent sounds i have heard is at open air venues.

 

Plus it would be hard for him to cut any squealing frequencies without affecting the whole mix.

 

^Hokum!
If you are talking about doing all that you need to get a monster mixer which has like 30 band EQ etc.

... surely not in the realms of 5K