I'd say you will use the stretchies overnight, maybe not at first when you are changing more often anyway but when the baby is a bit bigger and going longer at night without a nappy change, pocket nappies like the BG are unlikely to be absorbent enough, even with a booster. I would recommend getting some boosters though, Little Lambs bamboo boosters are good, i had to use them in the day with my daughter otherwise i would get leaks in about 1.5 hours - and the Easy Peasy hemp boosters are thicker and super absorbent for overnight. Used to use them in a bamboozle, folded in half under the popper-in bamboo booster they come with, and that would last all night.
With the bamboozles you should also use fleece liners, basically just a thin rectangle of fleece that you lie flat inside the nappy, it creates a stay dry layer against the skin. You can buy them or make ur own if you buy some thin fleece and just cut it up into rectangle or hourglass shapes.
Bamboozles are brilliantly absorbent, but they need about 8-10 washes before they reach full absorbency otherwise they won't last overnight. You don't need to dry them between washes.
Strip washing is basically a really thorough clean to strip out any ddetergent residue, smells etc. everyone seems to do it differently but I'd say a cold rinse with no detergent, 60 degree long wash with full dose of detergent, preferably non bio powder, then several more rinses til you don't see any more bubbles in the machine. If they smell of tergent when you get them out,keep rinsing! Some people also swear by leaving nappies outside on the line in the rain for a few days to get them smelling fresh. I've never tried it but heard it recommended lots of times and this is certainly the weather for it so might be worth a try if they are smelly!