1) Does anyone shift gears?
I do, but only use 3 of available 7 gears
2) Should we grease the chain and derailleur? If so, do we just use WD40? Lithium grease?
Lube the chain with any of a gazillion bike chain lubes. Use WD40 to flush dirt, sand ,etc. if present. Dry chain after a WD40 flush, then lube with chain lube. WD40 is not a good lube but is a great flusher. Just keep the deailleur clean. Tooth brush works fine.
3) Do you take the battery off when not using?
Always.
4) Can shocks be adjusted?
Front shocks are adjustible.