How long downloading takes depends on the quality of your link. But it also varies because browsers handle PDFs in different way: it may be better to download a volume yourself, so that you can then handle the file as you wish.
There is no reason why you should not download as many volumes as you have room for. Although much of the material is still in copyright (by the Abbey unless stated otherwise), all the material of volumes 1-119 has already been published in print. Having your own copy will make research easier.
This site, when complete, will contain 119 volumes. More recent volumes are published
on line here. The site would be much better if there were a general Index by Author, and by Subject, at least for the articles (and obituaries). But just now we lack the resources to achieve this: it remains an aim.