Correct but still to avoid rework do you recommend to go for higher memory configuration initially so that it will be some time before i replace the micro. And one more doubt generally what is the external oscillator frequency I have to select that is either 4Mhz or 8Mhz etc.
Ian's point is that there is no 'rework', you simply unplug one PIC and plug in another (that has the same pin connections).
As for clock crystals, it really depends what you need to do - for most application the internal oscillator is fine (as long as the PIC series has that).
I've recently (this week
) started playing with the PIC24/33/32 series - but mostly the 24. I've bought a MicroStick II which comes with four example PIC's, two 24's, a 33, and a 32. I've also built a further board for my tutorial series, and bought a few 24FJ64GA002 PIC's to play with.
All these PIC's have internal oscillators, avoiding the need for a crystal - unless you need high accuracy, and all are pin interchangeable.
Here's the design of the board, it incorporates a 5V regulator, and a 3.3V regulator (to feed the PIC), the power to the three sockets can be selected with a jumper as either 5V or 3.3V, and there's an LED (connected via another jumper) fed from the same pin as the MicroStickII board - so you can use the demo program that comes with that unit.