I may be being a bit dim, but I’ve not noticed any guide or anything about all these things like ADR and what is needed to carry load x and then what else may be needed to carry load y. Like for example, would I be right in thinking a particular certification would be needed to carry big plant? What about other cargos and substances?
If there’s a guide or whatever already on here then feel free to call me names as long as you show me where it is. 
a driving licence, would be your starting point, cat c and/or c+e then you can start thinking about carrying
loads. if you search about you will see that adr is for hazardous goods in tanks and packages, cpc is required to operate a haulage business, you will also have to complete your periodic training i.e, dcpc hope this helps you, search facility will give you all the info you need and then some
You are not dumb to ask,better to ask,then get stopped down the road by the old bill or vosa,or even worse in europe,the fines out there go in to thousands of euros,for sometimes petty offences.
Diesel dave,is the best to ask what kit for adr.
This PDF file may be a place to start http://www.dft.gov.uk/pgr/roads/vehicles/vssafety/safetyloadsonvehicles.pdf.