Speak to the girls at the FTA shop. They sell a system which is ideal for O/D use. I think it costs around £260.
You need to download your card every 28 days at least, and the vehicle unit every 90 (I think).
You are not obliged to have the information analysed, but you must store it on a memory card (which is part of the kit, as is a disc which installs the system to your laptop) and keep the information for at least 13? months.
The FTA offers an analysis service which is very easy and cheap to use, you simply export the data from your laptop to their system and they will provide a report.
As I say, you don’t have to do it by law, but, as a new operator, it will look as though you are taking compliance (how I hate that word) seriously.