What autel do I have to buy for key programming?

Buy im608 pro. You have diagnostics included too. 

For diagnostic perfect buy Gutmann Mega macs (one of the greatest tools for Diagnostic) or otherwise Launch X431.

If you want to buy IM508 than buy it with XP400Pro you have then the same Immo functions like IM608 but you pay less subscribtion (around 450$)