1) No, you dont.
3) I dunno, but a quick google search tells me that the puttygen GUI has a conversion function. also note that you can do this step on your client or host machine, it doesnt matter.
4) You can edit the authorized_keys file with any editor you want, just make sure it has the right permissions
1 - So then the keys will be in different formats? Why would that work?
2 - I've tried that function before when using different tutorial, but it didn't work.
3 - I think I'm doing everything right, but to no avail.