I can't answer your full question because my research has only been in UK records but I've experience mostly of Ancestry and a bit with Find My Past. These sites hold many of the same records but also different records so you need to bear that in mind before signing up and handing over a lot of money. The other thing is that, in my experience, the transcription differs from one site to the other. There's not a lot you can do about that and one site isn't better than another (all down to human input) but if you can't find an ancestor or a family on a census on one site it's very possible they've been mistranscribed but may be easily found somewhere else. I've found Green transcribed at Grun and Lee as See, for example. Good luck!