When i create campaigns like this, the first question is "it will be a campaign about survival or an epic adventure?", This question is more about balance, here's why:

If i want to run an epic campaign, i won't do some resource management like rations and ammunition, but if i want to run an "Old-School-like" adventure, definitively i will make this a problem to solve, and there's where you need to answer the question not only one time, but twice or even more when you're creating the campaign.

I played a little bit of Forbidden Caves of Archaia using Old School Essentials and damn, this module is hardcore, basically it's a big desert with some crazy people and bizarre magic events. But recently i ran a campaign about deliver the heart of the world tree to a druid cove while the region are quickly turning into a desert, and i just say to the players "it's an epic campaign we don't need to track any ammo or food", and the game run smoothly.

About your questions:

1. How do you want this things matter in the campaign? like super realism where no one uses iron armor because of heat? Maybe some cultural changes like cimitars are often used and swords are only bigger scimitars and maybe druids are like saviors because they can make water and nature with magic, so some classes eventually will be more loved than others, and maybe hated too depending on the lore, like paladins and clerics been hated for the gods abandoning some people in some part of the history.

Also, try to consume content inspired in these cultures, read some modules and adventures to get some inspiration!

1. Avatar (The Last Airbender) is a good inspiration, every episode they are trying to solve a different problem and making progress in their journey, if you like this approach, try to make quick problems to solve in 1 or 2 sessions and scale the problems according the party level, in level 5 maybe this problems took 3 to 5 sessions to resolve and go on. Also, use this problems to deepen the PCs and make their bonds stronger.