If you start writing in one category are you pigeonholed into that one for the majority of your career?
Don’t worry about that. Lead with your best writing, and if you wind up with an agent who can’t follow you into the other genres you ultimately explore, they’ll be able to recommend someone else for you at that point. That said, it is important to categorize your work when presenting it to agents (and editors). They’re going to have to sell it too.
Should you send your one page only after you have the body of work completed or after you have 3-5 chapters completed?
You mean your query? Don’t submit fiction to agents until it’s completed. (Nonfiction is different.)
Can you continue to send one pages of your other work to the same author representative (AR)?
Don’t continue to bombard the same agent (or editor) with additional work if they weren’t taken with the first sample. Exception: after a while, during which you improved significantly as a writer and your future work is much better, preferably as a result of feedback from agents or editors.
How does the conversation of a willing AR usually run between the author and author representative? 1) lump sum of money to retain the AR?
HELL NO. No No bad. Professional agent organizations like the Association of Author’s Representatives prohibit their members from charging up-front fees for good reason. No retainers. No reading fees. Never.
Is it wise to have a lawyer in addition to an author representative to make sure the AR isn’t taking advantage of a naive new-to-the-business author?
Getting a lawyer to review your contracts is always wise, but expensive. Do it if you can find a cheap artists’ legal clinic in your area. If you go your own, ask a potential agent about their sales record, training, and connections. Commission on a book sale shouldn’t exceed 15%, but that can be higher for foreign and other subsidiary sales. You know what, I’m going to write up a sample agent contract for you guys. And a publishing one. I’ll link them here when they’re up.