Hendon Archive Advice

Could anyone with experience in dealing with the Hendon archives please advise me on a potential visit please?
I need a whole bunch of building drawings and I want to make the best use of my time down there.

As well as any general advice in getting the most out of an archive visit, I have some specific questions please...

I want the most readable drawing copies possible. Is there any difference in quality between obtaining paper or digital copies of drawings or between smaller or larger printouts? Are digital any cheaper?
Anyone know the prices please? Couldn't find anything on their site.
Can all drawings be located using their A/M number or do you have to do some creative searching for some?
Are there cases of mis-indexing i.e. is it worth me going through everything I can, looking for that elusive plan or is it a case of "if not in the index then it ain't there"?
Do they allow you to purchase a copy of the microfilm like you can from the Smithsonian?

Thanks for any advice you can offer.

Dave