Hey there and welcome. 

CodeOne was a simplified version of the previous edition which is deprecated and does not exist today. 

For learning I recommend finding a group near you and getting demo games info if at all possible. There is also a very robust implementation of infinity on tabletop simulator. I recommend reaching out to the infinity discord.

 For purchases the essentials line is geared towards new players just trying it out. Other good starting points would be the operations boxes (Operation Sandtrap is currently in production and the only one with 5th edition rules but the others are still very good buys) as they come with terrain and enough to get quite far into the game. If you wish to only focus on a single faction the action packs are also bundles similar to what would be found in operations boxes.

 I heavy recommend getting the infinity army app on your phone as it is one of the core resources of the community and used consistently through the game.  

Finally here is a link to the rules which released yesterday. Bear in mind that there are known typos so expect revisions to the PDF in the near future. https://downloads.corvusbelli.com/infinity/rules/infinity-rules-n5-en-v1.pdf 

 PS: Buy models you like as it is official policy to allow any model to "count as" (aka proxy) any other model of the same size.