I think what the above poster is referring to as an ECA, or End of Course Assessment. This is little more than an regular essay, except its posted to you at a certain date to give it an air of exam pressure ie. you cant spend all 9 months researching that 1 question and get a great mark. These tend to be common in maths/science subjects. Its similar to a 'project,' which is really the arts equivalent. Your course literature should indicate if it is either of these.
Exams are different. All my exams will be held at the University of Manchester. I presume other regions utilise a range of regional centres, local universities, colleges and/or anything that is a big enough room. The location is irrelevant because the exams are centrally marked. I presume the exams will be just like my 'brick' uni exams, where the student body is split up and allocated to respective rooms. Its impossible for me to give you an estimate of how many people will be in your exam hall/room but if you make a journey to the location youll get a good estimate by the size of the room. At my brick uni, I had exams in tutor rooms in which there was just ~10 other people there, and some in the sports hall where the whole year group of ~200 sat together.