Usually, the N-Well got the highest resistance per square but worst accuracy so not many people wanna take that risk. The alternative would be poly resistors. According to TSMC documents, the Rsh of P- poly w/o silicide can goes up to around 1k ohms/sq while P+ poly w/o silicide is only slightly over 300 ohms/sq, for 0.18um. BTW, N+ poly w/o silicide got 200 something, nearly 300 ohms/sq.
About how to layout it out, there are couple books talking about resistor layout, capacitor layout, etc. You can probably check the book "The Art of Analog Layout" first.
About the size, if you are going to use poly resistor, I don't think the size will be too big compare to capacitors or inductors. I personally laid out couple 5x MOhms resistors but the capacitor wes the biggest area consumer.