It's crucial to get your submission as good as it can be before you send it off, and your comments on my previous post, Top five tips for submitting your manuscript, have sparked a few more thoughts - thank you for the feedback! Perhaps I should add these further thoughts to the original post – renaming it 'Top eight and a half tips...'.
Calling an agency to confirm name and address details is always ok. Although if you have a new edition of the Writers' and Artists' Yearbook – you'll find details there too.
It is possible to get a very long book published, but it's less likely. Printing costs are always a consideration for a publisher and a long book is going to cost them more per copy. They have to be confident that they will recoup this cost.
Editing standards do vary, but an agency will not reject a submission solely because it doesn't confirm to house standards. All an editor or reader asks is that you have checked your work for spelling mistakes, and have avoided major grammatical errors.
Paying for a professional opinion on your work can be very helpful – although not essential. This is a service I offer, but there are many others out there – just google 'literary consultancy' or, better still, use the Advanced search on this site and you will find a plethora of options. It's rather like finding an agent: you should compare the consultancies' styles, see who offers what you are after, and give it a go with one you feel comfortable with.
Good luck with the writing!