Any arena and floor mods you had installed in 2K12, you can just copy-paste over to 2K13, so you may want to add this note to the top post.
Also, CFs and Jerseys are very easy to convert this year, since the Chinese 3DM Mod Tool works in exporting/importing textures already. An update to the regular Mod Tool will make things easier (or a translation of the 3DM one :P).
So, with that said, here's a few links I want to post, up to you whether you'll get them some prominence in the first post:
NBA 2K13 Mod Directory
I've taken it upon myself to keep this updated right from the start, with all the modders and mods of the NLSC.
http://forums.nba-live.com/viewtopic.php?f=149&t=87962
NBA 2K13 Community Modding Projects
A new initiative that invites the community to work together on modding projects. These projects are based on the principles of open-source, so all research and work done will be public, so that everyone can learn, and help.
http://forums.nba-live.com/viewtopic.php?f=149&t=87977
Current Modding Status
After just one day of NBA 2K13, we're starting to create the resources on how to mod this year: what works from previous years, what doesn't, what you need to do.
http://www.nba-live.com/nba-2k13-modding-status/
NBA 2K13 Modding Tutorials
As always, our approved list of modding tutorials should help you get started to create your own mods!
http://forums.nba-live.com/viewforum.php?f=150
...and of course
NBA 2K (Kinect-like) Speech Recognition Tool
My very last project for NBA 2K12, works out of the box with 2K13, and allows you to use any PC microphone to run plays, and basically do whatever button combo you want by voice.
http://www.operationsports.com/forum...d.php?t=581686
Hope this makes for a good start! Let's have another great year!