After several stays in the Marriott Resort, I would also say that you shouldn't pick this junior suite package.... as far as I know there are no Junior Suites with immediate river view in the Marriott Resort.
I would book the standard room package and maybe in the same time politely ask the hotel via email if they can offer you an upgrade to a Deluxe River View room (either because of your status or a slight upgrade charge - very probably they will give it to a Plat for free). And you could ask in this case to get a corner room... I think room number 463 or 464 or 466 (not sure anymore.. maybe someone can help) in the South wing is a very nice corner room. I had the room next door once and had a quick look into the corner room when the cleaning woman was busy. Looked really nice.
A taxi from the hotel to the airport costs 400Bt. ("hotel rate"), but you can also demand the taxi driver to go on meter which makes ist more cheaper (probably 250-270bt. something).