I think you are talking about wilderness backpacking, as opposed to regular backpacking.
Backpacking means you are generally on trails and bringing everything you need, including food. You don’t need survival skills to backpack, but some basic ability to navigate with a map and compass is really good to know.
Wilderness backpacking is like regular backpacking but is more survivalist and you generally don’t use established trails. This is more hardcore and can include having to get food while you are in the wilderness by fishing or hunting.
Start off hiking.
Gear is a big topic of debate. Understand whatever you buy will probably not be what you will need and you will probably replace or upgrade gear a lot as you find out. I don’t think anything I have in my pack now was with me for my first trip.
Bivy vs tent vs hammock comes down to what suits you and the environment you are going to, can’t hang a hammock if there aren’t enough trees.
Alcohol stove vs fuel stove vs cooking over fire all depends on your convenience desire and if there are fire restrictions. Hell, you can even go no-cook meals if you are indifferent to the comfort a hot meal on a cold day can bring.
Passive vs manual water filtration is a matter of personal preference. Water purification tabs are light as fuck, but the taste is not pleasant. If you have a good filtration system the source of the water need only be unpolluted, like a lake or stream. You can boil water, but that isn’t a perfect system and there is still a lot of junk and flavors that you probably don’t want. Pump filters are faster, but gravity filters require less energy and you can use them while on the move.
Shoes should be hiking shoes or boots, ones with ankle support can be really nice in topography where you will be changing elevations a lot.
Backpack should be an appropriately sized backpacking pack with a frame. You can go frameless if you are ultralight, but ultralight people are neurotic and derrainged. You want one that fits you and is big enough for the trip but not oversized.
Food is pretty personal. You really could only take highly perishable foods like unpreserved meat for a day if you are in temps above safe storage temps. So don’t think you can take a steak for day 4 when it is 25C out. If it doesn’t need refrigeration or is a preserved product, you can choose what you want. Some people will eat nothing but trail mix, some people will take nothing but dehydrated camping food, what you take will be up to you. If you are looking to cook whatever you want, then overlanding type camping or car camping is what you should be looking at.
Definitely understand that the temps that a sleeping bag are rated for are not accurate. Whatever the lowest temperature they say it is good for is almost barely survivable in reality. If A bag is rated for 7C, it probably is livable at 13C with layers on. Bags are case by case so you will have to try out a bag to know at what temperature you can comfortably sleep in them.
You should start with reading forums and communities to see what other people are doing. There are checklists you can reference to wrap your head around everything you might need and then you can figure out what you want. Definitely start with an overnight trip to work some kinks out of your setup and then go for more days as you gain confidence in your setup.