pic microcontroller based temperature monitoring and control

[scientistumair]

I am new in microcontroller. I have task to design pic microcontroller based temperature monitoring and control using pt100 as sensor. Total 8 pt100 are to interface with pic16f877a. Set points are to be given by keypad and display should be on lcd. Control technicque should be pwm. I am using CCS compiler

First: I am controlling and display 1 temperature (i.e. using 1 pt100)
Can single pic16f877a controller can do this task?
I have following difficulties:
When I interface pt100 to pic then my pic doesn't read analog voltage voltage drop to constant -0.875 volts at input of microcontroller.

Circuit is as follows:
1ma current source-voltage follower-noninverting amplifier-pic16f877a.
I am using lm324 quad opam ic for current source and for amplifier.

Second: How to develop variable pwm in pic using pic (difference b/w set point and process variable=pwm duty) ?.

Third: How to interface keypads. Should I have to interface rs485 for communication?

[FvM]