It could certainly be a hoax. I am open to that.

I share the skepticism. It could have been a CBS planted hoax. A total made-up hoax based on no real info would not have matched up as well with the contestants, so it either genuine or an insider hoax.

I can answer part of your questions, so we can see how much of the real concern remains.
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1. How and why does this random person know where the crew was staying in Samoa?

Answer: I knew it, and everyone there would know it. There is only one resort of any size on Upolu, and that is Aggie Grey's. It was much publicized for the first filming of how weddings were ruined that had been planned for months when Aggie's emailed customers with pre-existing reservations and said they would not honor them due to Survivor fully booking it.

In fact, spoiling the place the crew stays is one of the ways to confirm that a location is hosting Survivor. I did some of that with Cook Islands.

In sum: not an issue

2. This spoiler was posted at RFF on Aug. 20th. Travel was aware that Coach and Ozzy were cast for season 23. I'm not sure of the exact time frame but Aug 20 was around the time that CBS revealed that Coach and Ozzy were cast for season 23. If this info was released by CBS prior to Aug 20 then it had been out there for at most only a few days.

A: not an issue. Dani at Skills broke the Ozzy/Coach spoiler on May 24th, and it was discussed all over the boards for almost three months prior to this post.

3. Travel, who posted that he was staying in Samoa, decides to take a plane to Fiji and just by coincidence ends up on the same flight as the pre-jury booted contestants. Why would Mark Burnett Productions even allow Survivor contestants to fly on public flights rather than hire a chartered flight to take them to Fiji? Also, the chartered flight would probably be cheaper.

Travel said he/she took a day trip. I wouldn't put it that he just coincidentally ended up on the same flight. More like, on the flight, it happened there was a reality TV fan. Because the fan saw something, he posted. Not like the fan was hoping to get a spoiler and just happened to get the right flight.

SEG has been flying contestants on public flights for all this time. There was, for example, a flight spoiler for the Outback. IIRC, at that time the jury and pre-jury flew home separately. After that, they flew together back to the USA so that they would be in one group.

I think that due to the fact the contestants are unknown to the public at this point, the producers feel the cast will not be obvious.

As for the Fiji resort, it is VERY close to the airport, so it is ideal for both a quick getaway and for a place to hold the contestants prior to flying home. I checked out the travel forums for that area. This resort is not obscure and has plenty of buzz. There was some construction going on during this period, and that put some people off. However, it was open to the public.

Point: There should have been other people there.
Point: It is barely possible to do a day trip to Fiji given current flight times for Air Pacific, the only nonstop flight. On Fridays, the flight does not leave until afternoon, and returns after 2 am Saturday, and it costs about $500.

4. As a second coincidence, Travel hires a driver in Fiji who takes him to the same semi-secluded resort where the castaways are staying and that no one else is staying at this spa other than Travel and the 5 castaways. Now Travel is staying in Fiji when at the beginning of this post Travel said that he was staying in Samoa.

No, Travel said he went to a spa in Fiji for the day and was posting at RFF from Aggie Grey's the following day.

5. How does Travel know that these people are not friends when he says that they are all under 40 and "actor looking"? I could see this being concluded if the 5 were a mix of young and middle-aged.

Mmm, well I give benefit of the doubt that in-flight observation led him to conclude the group was something else, and I think the Survivor presence plus the Americans with a Kiwi "handler" was the tipoff.
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The more carefully I read this, the fishier it gets. The tweet by Christina Cha that indicates that she was a pre-jury boot seems more reliable than Travel's post and she was not likely to have been one of the 5 sighted by Travel.

Agree about Christina.

My main reservation is that the day trip story is weird, because of the flight times and the expense for very little payoff, unless the person works for an airline and can fly standby. OTOH, a hoaxster could have easily made a story without that issue, and the flight times may have changed since last August.

OTOH, if you follow RFF at all, the TAR forum, you will see that on about half the legs flown by TAR and the tasks too, there are fans around the world who see the filming and tweet or post about it. RFF is a network of fans that stalk TV productions on a global level, and there is nothing weird about a fan happening on a bit of Survivor and taking it to RFF right away.

My guess would be that if legit, Traveler is some other RFF poster who is a regular, who decided to use a ghost for this because SEG has started suing people who post spoilers of their show.

Or it is a hoax, or it is a crew member having a laugh. If a hoax, I believe it is an inside job.