Same difference I would say.
Just one is for data and the other for voice data.
No not quite, both are capable of carrying data/voice/video the main difference is that the Leased line is dedicated (its yours to use as often as you need, for a fixed fee), whilst the ISDN is a shared service (you contend with others for the service and the more you use it the more you pay).
Not sure about E1 vs. PRI E1, but in North America, a non-ISDN T1 is channelized (24 channels). Each channel uses robbed-bit signaling to indicate an on-hook or off hook condition. A non-ISDN T1 can handle analog voice and analog data.
For a PRI T1, it's still 24 channels (23 bearer channels and one D channel). The D-channel (channel 24) is used for signaling. In fact, one D-channel can handle the signaling for multiple T1s (e.g. one D-channel could handle signaling for three T1s. In this way, you gain two extra channels on two of those PRIs, as you don't need a separate D-channel for each of the three T1s). A PRI T1 can handle voice and digital data.
I'm guessing the E1 vs. PRI E1 would be similar.
Not wholly accurate, as all analogue voice is converted into a digital format for transport over the wide area, with the channel bank responsible for taking multiple analogue voice channels, digitising them and then multiplexing them onto a high-speed digital link, hence a T1 can be provisioned with ISDN (PRI or NFAS) or non-ISDN (T1 CAS) digital signalling.
An E1 operates at 2.048Mbits/s and consists 32 timeslots, as opposed to 1.544Mbits/s and the 24 timeslots of a T1.
An ISDN PRI in Europe is 30B+1D channel.
Whilst synonymous with voice, an E1 or T1 is essentially a high-speed digital WAN link for transporting data in all its forms.
At the physical level nothing. PRI are normally channelised and generally go to the telco public network. E1 can be channelised. PRI use channel 0 and channel 16 for special purposes. It more of a use issue.