iPod rechargable any time during cycle?

lithium ion batteries (like in ipods, laptops and cell phones) should be charged frequently at any charge level. they will wear out eventually, but draining them between charges is harder on them (unlike the old ni-cad "watermarking" ones still used in some cordless phones).

it is a good idea to drain and charge fully once in a while (once a month or less) mainly to calibrate the charge level meter.

No, just use the iPod and don't worry about it. Run the battery down completely once a month or so until it shuts off to keep the calibration current, if you so desire. If you don't, it's not a big deal. Lots of people have spent lots of money improving batteries over the years, and memory effect is not a serious concern. Calibration is only necessary if you feel like battery life has shortened substantially.

Plug it in when you want to transfer data, plug it in when the battery is lower than you'd like it to be or when you're going to be away from a charger for a while. The time and energy spent trying to tiptoe around unnecessary procedures is greater than any potential loss.