The uC is chosen by means of the requirements, if the project is operated by batteries then go with MSP430. But hey, this is an 8051 forum. So if you are going to choose a 8051 you bet we can help!

Many uC has now integrated ADC. 8051, AVR, MSP430, etc.

Please don't use SMS it is quite annoying to try to understand them

Why do you suppose you need a 16bit micro? you need to describe better what you are going to do

Please specify more about your "AC" plant. What is an AC plant?

And try to answer the other post so they can help you