[Elecraft] Purchasing K3

[G4GNX]

Hi all.

I'm about to buy my first (used) K3. The only known issue with it is a small 
crack in the knob on the 2nd VFO, which should be easy enough to replace?

I also have the serial number and I know its history. It was purchased in 
the UK as a kit and assembled by a local ham (now silent key). There's no 
microphone with it and no serial cable., but it does have a power lead and 
the 100W module.

I'm assured that it's fully working with no known issues and I will be able 
to try-before-buy.

Questions:

How can I find out what year it was supplied, from the serial number.

Is there any point in checking its current revision level, or should I just 
download the latest firmware and install it?

Are there any known issues that I should especially look for?

My preferred method of connection to a PC would be a USB cable. Is there a 
mod to allow USB direct to the K3, or is my perception of the manual correct 
and I need to use a USB to Serial cable?

I presume that I will have to order a front panel microphone plug from 
Elecraft, in order to use one of my electret microphones?

Thanks in advance.

73,

Alan. G4GNX