If I want to isolate my cards (galvanic),then is it necessary isolation between analog input section(amplifier and ADC) and microcontroller section and
RS485 bus??(between three parts)

Or is it enough to isolate between analog section + micro and rs485 bus??
Both the uC and the RS-485 are digital, thus no 'isolation' is required (I am talking about separate ground planes etc). If the difference (spikes and permanent) between ground at point a and ground at point b is no more than your 485 transciever can handle as common mode (see dataasheet) use a 'normal' 485 transciever. If it is more, Maxim has isolated 485 transcievers that, as far as I remember, can handle +-60V common mode (see www-maxim-ic.com )
Under no circumstances will you need to 'isolate' (in any way) between your uC and the 485 transciever.

Erik