I'm in the process of changing all my doors over and have been told by
the joiner to get hinges that are roughly 100x60.

Couple of questions.

Toolstation only list one of the dimension sizes on its hinges. I take
it they are proportionate so 100mm will be roughly 60mm on the opposite
plane?

http://www.toolstation.com/shop/p13985

Also, loose pin hinges, are these for being able to lift the door off
without unscrewing the hinge?
Does this make them slacker than normal fixed pins or is there any
advantage / disadvantage between the two types?

Thanks.