Not necessarily. There are dozens of horses, hundreds of outfit combinations you can make, and a hell of a lot of guns to start. Sure, you get access to them as you progress through the story, as several are locked in the beginning, but that doesn't mean you can't kill someone and steal their guns afterwards. Not to mention stealing their horse. You can then sell the horse to a stable, but you usually get $5 or less since you don't have papers, unless the horse is a high quality breed, which is rare. The gun you can take to a gunsmith and customize everything about it. The metals, varnish, engravings, carvings, rifling, sights, literally everything. personally I recommend buying it when it becomes available, but sometimes that isn't the best option as you might need the extra power that a stolen gun can give you. You can't sell your guns, but you can store them in your foot locker at your tent in camp.
There's a world of customization, and endless options to make Arthur a reflection of yourself.
Unless you want to make him female. Then you're screwed.
😢