1. I would go with whatever publishing company I could get, but I would do #2 first, see below.
2. Get an agent by submitting letters and sample chapters to reputable agents--and any agent or agency that requires up front fees should be avoided at all costs. A good agent will NEVER charge you unless you actually get published--which is their job. When you get published they get a percentage of your profits, which is industry standard, and the reason why you get an agent--they have the best resources and the inside track on getting new authors published. That also means that it is in their best interest to get you published by the best publishing house available, one in which your book is likely to earn lots of money--and open the door for you to submit another book.
3. It is possible but extremely unlikely for a first time author to make over a million dollars for a single book. There are well known authors who still don't make a million dollars a novel. Super rich authors like Stephen King are actually very rare, so don't quit your day job.
ps. If possible, try to never sell rights to your novel. EVER.
