Dude, it's a simple adventure and exploration of unknown territory. Yes, people are normal there's nothing particularly wrong with that factor. The main point is to go out into a new and dangerous territory and try to survive and find out new mysteries and treasures along the way from possibly past civilizations? Could there be mystical elements in it such as curses and perhaps golems, or even minor levels of magic? Sure but it in itself should not be a main element, and it should not be a main element in the characters themselves. Nor should asking 'how would they survive' because they're normal something to use in order to introduce larger fantasy or science fiction elements into a regular modern or historical roleplay. The 'how' and 'if' they survive is determined, in said roleplay and seeing as humanity is still around today, and has explored various regions, I think it's plausible to be fine.
If you want to set up a fantasy adventure, go ahead but make a 'fantasy adventure'. If you want your characters to have a gun, or a sword, explain why they would have it and perhaps what kind of weapon it is which can make things all the more interesting, even if it is a simple reason. Such as it being a family saber and a musket being provided for the safety of travelers in the new region, or an assault rifle and the sword being used in place of a machete to cut through or deal with excess plant life and so on. I would recommend a more historical adventure setting as it seems to make more things... interesting and harder to combat. Using a modern setting with modern weapons and supplies still has difficulties but it may seem easier dealing with wildlife using a shotgun (ya know?) though this could be dealt with larger threats and more dangerous company competitors.
Making up new characters, to fit this is also fine and I would say would be smiled upon. In all honesty I do not want to deal with characters with strong powers in this, especially having seen an example of such. No one is claiming it has to be Joe smoe that regular guy from down the street, hell it could be one of the world's strongest wrestlers, or a researcher who looks to adventure into more dangerous flora and fauna life for medication and is used to hunting, etc, etc.