Slightly mixed up, too.

A licence is basically what gives someone the permisson to fly an aircraft. Any pilot needs a licence. Licences do not automatically imply that you might fly for commercial purposes (e.g. think of the PPL). To do this you need either a CPL(A), a frozen ATPL(A) or an ATPL(A). Any licence can have either mandatory add-ons or non-mandatory ones. An example for the former would be that you only get a CPL(A) if you succeed in getting a long range certification at the same time. An example for the latter would be a multi-engine rating (though I agree that the use of ATPLs is slightly limited if you do not have ME ratings...).

Now wrt ratings: Anyone having even the "highest" licence, aka an unrestricted ATPL(A), may not fly any aircraft having an MTOW > 2 metric tons. If I like to do this I'll need a type rating for the corresponding aircraft. This works fine even for holders of a simple PPL - at least up to an MTOW of 7.5 metric tons. Now for any plane having a larger MTOW a two-people crew is mandatory acc. to JAR-FCL. The trick being that at the same time any aircraft requiring a two-people crew may only be flown by chaps having a CPL or ATPL. So no PPL holders will every legally fly planes > 7.5 MTOW.