I haven't had an issue with printing PETG with my stock hotend on the Wanhao. Some people swear by the Micro Swiss hot end and others do not. They do have pretty good customer service from what I have seen. I suggest you start with PLA and its a pretty easy material to print with once you get to know your printer move to other materials. My dad swears by PLA+ as it has a little more flex to it and he gets great prints on his printer.
The E3D hot end is quite a bit different than the MK10 on the Wanhao, There are people who have printed new x carriage to make it work (See Thingiverse). You sacrifice some of your printable height envelope to do this. I don't think I would attempt it without having a second printer to print parts for it while doing the conversion. It's a PITA to dissemble the x axis and you would have to do this a lot with a single printer.