You don't have to downgrade at all. It's an optional step in the 4.3 guide but it's really up to you. Welcome to the site.
Welcome to the community! Members of the community are extremely helpful, and there is information throughout the site on just about every issue you could imagine. Make sure you read ShadowSonic2's Wiihacks Ultimate Index. Here are a few things to help you get going:
1) Read the Rules of the site. They are important and there are consequences to ignoring the rules, not that you would do anything like that.
2) Read the Tutorials and Guides.
3) SEARCH for questions you may have before starting a new thread. If you would like to narrow your search, choose the option on the search page that says "Search Titles Only."
4) The advice on this site is all free, but it does cost money to operate. If you're able it would be greatly appreciated if you DONATE.
It is NOT advised that you update to system menu 4.2 or 4.3 at the moment. Although they can still be modded, their only reason for existing was to eliminate the homebrew channel.
If you have not softmodded yet, there's an excellent guide by dogeggs for system menu 3.1-4.1 FOUND HERE
And a wonderful guide by messie for system menu 4.2 FOUND HERE
If you were softmodded with a working homebrew and updated to 4.3 then you can use THIS guide to restore your CIOS.
If you have a virgin wii with 4.3 then use THIS guide to get going.
Any other problems can usually easily be found by searching.
Feel free to join us on the IRC!
If you use Chatzilla go here: Chatzilla
If you use mIRC go here: mIRC
If you're having an issue with a certain game, ex: New Super Mario, Monster Hunter Tri, Super Mario Galaxy 2.... Take a look at this list of games that have their own guides on getting them to work HERE. If you still can't figure it out make a post in the guide for that game for assistance. Please do not start a new thread on the game as it only serves to clutter the site.
Again, welcome to the wiihacks community. We hope you enjoy your stay!