Range will depend entirely on wind resistance.
For upright bikes, perhaps with some panniers catching wind, tall handlebars, I can give you some ballpark numbers for how many watts a certain speed takes. Add or subtract 200-300w for a slight uphill grade, or much headwind. Rolling hills tend to even out, coasting down almost for free even without regen. Many stop signs or lights can also eat up 20% of your range compared to rides with a stop only every couple miles.
No pedaling.
15 mph, as low as 200w. So the math would be at 15 mph your 300w of usable battery should last an hour and a half of riding. So 22 miles maximum, then subtract for wind, hills, stops, etc.
20 mph 400w
25 mph 650w
30mph 1000w
Just my opinion, that nimh pack is going to be a pain in the ass. you can paralell them to discharge, but you must charge them in 1s strings.