1. Yes, all of the steps are necessary, but where you start in the guide depends on the status of your 3DS. If your 3DS was hardmodded or happened to be 2.1 or lower firmware, you could downgrade to 2.1 via hardmod, dump and backup the OTP, update to 9.2, back up your SysNAND, install A9LH, then update SysNand to 11.0. Nothing will get faster/safer unless we find bootrom one day and/or a more reliable exploit for downgrading, but every step in that guide is done for good reason.
2. The files you should truly keep are SysNand.bin (the first one you made before formatting, otherwise EmuNand_original.bin) and otp.bin: Everything else is secondary/can be recreated easily if you just have those two files. (You don't need to keep your otp.bin, but you will regret it if you ever need it again, because it takes quite a long time to obtain that file) Of course, my information could be outdated from the current guide, because I did this a few months ago and software had been updated by then.
By the way, you can .zip/.rar/.7z your NAND.bin dumps to save computer space. Also, the guide tells you what you actually need to keep on the 3ds at the very, very end of the guide in Part 5.