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Try to at least leave access to the cistern, if it starts to fail you don't want to have to destroy your tiling.
Definitely do this, and make sure the internal overflow sits below the holes at the top of the cistern too. Whoever installed our bathroom failed to do either :|
e: read to the end, obviously you mention this because you're not an idiot. Unlike whoever installed our bathroom.
6pt-
You did make it clearer the mistake people make though, the water flows out of the screw holes long before it goes over the top of the cistern. I assume the people who make the cisterns don't talk to the people that make the syphons, or they're made for a variety of cisterns. You can see why an installer would assume that a cistern and syphon supplied as a unit wouldn't overflow through the screw holes.
The other issue though is flow rate, if the overflow flow rate is lower than the incoming you have to lower the incoming rate. Happened to a friend on their top floor toilet while they were on holiday just after renovating the entire house, ruined every room in the house.
Airhead
I've never fitted one offset, it would be an experiment. Usually you use a solid pipe between the cistern and toilet, I guess that's got something to do with the water pressure of the flush. If you changed to flexible it would have to have 2 solid ends to connect to pan and cistern.
I usually pay £80-£100 for a hidden cistern and they are mounted on the wall with a couple of screws, the quality of the internal mechanisms & single or dual flush is probably why I spend more than £50. The expensive frame ones are normally used for pans that hang off the wall with no pedestal.
Having a hidden cistern just means a bit more of a fiddle for maintenance, if possible ensure access to the back of the toilet from a hatch or fit a flexible pan connector so you can connect the pan before pushing it to the wall. Try to at least leave access to the cistern, if it starts to fail you don't want to have to destroy your tiling. I've done a few where it's tiled behind the pan with a wooden top and white glass (I.e. No green tint) painted on the back. That way you have a nice waterproof surface but you can lift it off, unscrew the wood and get access to the plumbing.
Also check that your overflow, which should be internal I.e. Flows into the toilet not a pipe outside can evacuate water as fast as the feed into the toilet. If the inlet valve fails to shut off you don't want water overflowing the cistern. In fact everyone should hold down their ballcock and see if there cistern overflows, it's suprising the number that do.
Apparently flexible flush pipes are a thing, so you can have your offset cistern.