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 pic 16f877a can do this task?
I have following difficulties:
when I interface pt100 to pic then my pic doesnot read analog voltage voltage drop to constant -0.875volts 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 cycle)
Third how to interface keypads.Should I have to interface rs485 for communication?