you are keeping withing the same tint bases it sounds like, so you should be fine to go ahead with your new color and also you mentioned your previous color was an eggshell sheen. I would however suggest making sure your walls are clean and dust clean; after all this is is a bathroom that gets frequent use and is subject to sprays, lotions, oils, toothpaste, zit cream on the wall or cleaning materials that may have bounced over on the wall where the toilet is . Believe it or not I have been in homes to redo the baths and well lets just say if there are little ones or may have missed the toilet . No offense men, but it does happen. :) I have seen quite a few head scratchers in my time. I am sure you have already taken these precautions and are aware of the pre prep. good luck. It is not necessary to prime each time on a job. Every job needs to be evaluated on its own findings to determine a primer and the type of primer to use. :)

BIN you need if you have to cover knots and that can be used as a spot primer. Otherwise, Zinnser, or Fresh Start is good. Where I would spend the money is on a decent trim paint. I almost always use BM. No need to remove trim, sounds like you are on the right track!

If I were you, I would use the SW ProClassic paint as I think it gives a smoother, silkier finish. But be sure to take off the cabinet doors and paint them horizontally. I think the paint salesman was suggesting a "blocking" primer rather than a bonding one. All primers are supposed to bond. He might have been suggesting ProBlock Primer which I have used over stained wood I wanted to paint white. It keeps the wood stain from bleeding through. There is another current thread going on about painting cabinets and you can learn a lot from it. So rather than inventing the wheel, read this: http://ths.gardenweb.com/forums/load/paint/msg0713562232723.html?10

When they say don't "cheap out" LISTEN!! Take my advice, I learned the hard way. You can a) paint one coat of cheap-y paint, and then re-paint it year after year, and re-scrape, and get a sunburn and waste weeks on end, or.... b) pay the money up front, and do it right. Expensive lesson, especially when you are painting a huge garage. DON'T use those vinyl spackling buckets that cost 2.79. Get good exterior caulking, whichever one costs the MOST is probably the best one. Be patient, just let it dry all the way. Scrape off EVERY peel, no matter how long it takes. If it's REAL bad? Get the spray on stuff, and get every last bit off. That's what I wish I'd done. And I did scrape to bare wood, but used crummy spackle and crummy paint, and one coat. Saving $50 on paint and materials is now probably going to cost me 16 hours time, and over $150 to fix. If I could afford it, I would spend $2500 to side the thing and never do this again. Spend the money up front, take your time. A GOOD paint job will last 10-20 years. Mine lasted 16 months, and looks worse than when I started. And I had professional help. Who told me to buy the good stuff, and I ignored him, thinking how smart I was. And don't try to paint outside when it's 80 degrees. ACHHHHHGGG!