OK - its not rocket science, I will try to anbswer all your questions
1 Bumgenius is a stuffable nappy - the absorbent bit goes inside the pocket so you can remove the wet pad a refill to reuse the outer, or, like me you can throw the whole thing in the bucket and put on a fresh one. Stuffables are good because you canhave a pile ready stuffed and simply take one off and put next on like you do with disposables.
2 Pop-in nappies are made by Close parent and if you have the original ones the inner part, which can popper in/out, is made of bamboo which is really good and absorbent (DD could wee through a BG depressingly quickly) Again you can take out the poppered in absorbent part and reuse the outer, but you don't have to.
3 - Liners. I use disposable liners to stop the wet feeling against babies skin, and so when there is a poo I can just lift the liner out of the nappy and flush it before putting the nappy in the bucket. You don't actually NEED a liner with the BG as the fleece side of the pocket stops the wetness against babies skin, and poo shoiuldn't stick to it - but I like liners! You just need to be careful that there are no corneres of liners sticking out of the nappy at the legs as this will make the wet wick out against his clothes and look like the nappy is leaking. Withthe bamboo in the pop-ins you will need a liner but they are easy to tuck around the insert so less risk of them poking out of the elsastic on the legs.
4 Washing - Do NOT use fabric softener.
Use non-bio washing powder, about half the recommended amount on the packet to avoid soap build up on the nappies.
Putting the nappies through a cold rinse cycle before washing can help if they start to smell of wee - seems to be a problem mostly with man made fabrics
It is nice to use a sanitiser in the wash
I wouldn't recommend tumble drying the outers, although it may be quicker to tumble dry the inners of the pop in nappies as bamboo is slow drying because it is so absorbent, the inners for the BG will dry pretty quickly just over an airer.
5 Storage - Did you buy a bucket when you bought the nappies? Just throw the used nappy in the bucket and put the lid on, I wash every other day. Some people like to put a few drops of essential oil in the bucket to mask nappy smells but I don't find it necessary. You do not need to soak the nappies while waiting to collect a washload.
6 Prewashing - the bamboo inserts in the pop-ins will get more absorbent with use so it may be worth washing them a few times before using them
Hope I haven't confused you too much, any more questions just say :)
Well done for trying them and not just ebaying the lot!