No need to apologize. We all started somewhere. I have been hacking for a couple of years now, and I still have a lot to learn. I just wish I had started posting on WiiHacks.com sooner, because I have learned a months worth of information in only a few weeks. There is no need to update to 4.2 (and definitely not 4.3!). SM4.1 has all the latest features, so you won't be missing out on anything.
As for the guide, you should be safest if you start the guide from the beginning and work to the end. You will probably end up repeating things you have done in the past. That won't hurt, as long as you follow the directions correctly. Anything old will be overwritten and updated.
Don't delete/overwrite your NAND backup if you made one with bootmii.