Money: 100k for at least one month, doesn't mention extra pay for extra months.
Splitting:
Like Ten-Hex said, if anyone gets in trouble, they're at half force defending themselves.
Merging the groups on the island? If the party that's registered in their system is spotted anywhere near bunch of enemy infiltrators, their SIN's, descriptions etc (which are in the system) are immediately forwarded to every other Aztec facility, governments and security agencies; marked as spies/terrorists. Erasing that wouldn't be a possibility anymore.
Mercs: weren't WE hired for this job? Seems like Johnson is expecting sabotage instead of war.
Pirates/terrorists: I don't trust them at all. And sure they can target the island. But islands are pretty good defensive locations, a couple of small attacks, sure, but shutting it down for a month would mean laying siege, not exactly the guerrilla hit&run tactics pirates/terrorists are used to. Aztlan will get backup the size of a small army there in a matter of days and wipe them out. Selling them the info as paydata and buying some extra days of 'delay' in that same deal, sure. But I don't like it as the only plan.
Bus:
Metagame: I wanted the tour operator bus thing because I was hoping Chrona didn't waste half his character, heh. Also seemed very plausible that way. I don't know any safari park where you can't drive in your own vehicle... Of course there's an option to hire bus transportation for guided tours, but that's not mandatory.
Game:
(they do list bus rentals for tour groups)
Is there a source of important info I'm missing somewhere?
Anyhow, so 'tour operator bus' is out of the window. Don't have chameleon coating, but we have time for a paint job. Of course, if they used any other brand than Conestoga, we're screwed. Even then, how do you explain another bus exactly like theirs suddenly arriving on a ferry? Successfully smuggling a bus seems near-impossible, but sure, let's assume that works: How'd you explain that their bus depot which always has their own X buses parked there at night, suddenly has X+1 buses there?
How do you hide an elephant?
You don't, that's just silly.
Jeep: Sure, in 250km2 we could hide it somewhere. Using it as transportation: run into a guard, tour bus, camera or anything and they'll be hunting. Add it to what list of vehicles? Again, who knows what kind of vehicles they use there, or what they look like.