It's astonishing what you can find online. I've only gone back to
1464, but I use Google earth for landscapes and Google Image for
old maps, pictures etc. (which can often lead you to a site too, of
course), and there are vast amounts of documents online. The
problem with 13th century is that unless your Middle French or
Latin is pretty nippy, you'll need translations. But Project
Gutenberg should be able to help there.
Google Scholar is good if you want to make sure that what you're
reading is scholarly and genuine, but Wikipedia (though to be used
with caution) can be very useful, but the more egregious mistakes
have usually been pounced on by someone, and it can certainly give
you an overview and then steer you towards more reliable sources.
The online archive of the Times Literary Supplement is a goldmine,
because their reviews are usually by specialists in the field (e.g.
Mary Beard is their editor for Classics & Ancient History) so
often present a pretty good survey of the subject of the book
they're reviewing, as well as saying whether the book's any good.
The History Today archive is another goldmine - specialists writing
for a general, interested audience - and you can buy individual
articles. There used to be a wonderful site called Deb's Historical
Research Page, stuffed with links to individual sites about clothes
and food and currency and so on, but sadly it seems to have
vanished.
The other thing to do is to make best friends with your local
library or better still a university library. That's not just to
borrow actual books, and journals (it's journal articles which, at
a guess, will be your biggest source) but also because it should be
a portal to the academic online collections of journals - JSTOR,
HUMBUL, and so on, which you should then be able to access. And
there's nothing to stop you emailing an academic who works in your
area - they, too, are often thrilled to be approached, although be
prepared for them to be
extremely twitchy about any which
you might want to - yanno - invent...
The other thing is to look for online forums of people who are
interested in your period and people - it's amazing how the Net can
bring obsessives together, and their nerdy hearts are thrilled when
someone comes bobbing in asking a question. The Historical Writers
Association, which is relatively new, has a forum which is open to
all
http://www.thehwa.co.uk/forum/
and you might find others who are also researching in your area and
could point you to good sources. Though you just might not want to
be too specific about who you're writing about: really juicy
historical figures are in short supply...
I write first drafts longhand, and type up as part of the process
of revising that - I then work on hard copy at various stages too.
But everyone's different.
Oh, and don't forget to start saving for a research trip to Europe

some time. Which is tax-deductible,
of course...