Don't worry about dust, just change lenses whenever, wherever. Unless there is so much dust, pollen,
spray from waves of the sea crashing that you can see the particles in the air. Even in those situations, I've taken the risk in swapping lenses, because I wanted the shot.
It takes a LOT of dust in the camera body to gum up the works, or be visible in prints. My first DSLR made it to 80k before the mirror wouldn't reset. My second got ran over. I'm on my third DSLR living by the camera
philosophy of Ken Rockwell: don't baby your gear, get out there and wear it out. You will miss opportunities if you carry too much or are too protective.
I recommend the Eyelead Germany sensor cleaner, but wait until you actually have a dirty sensor before buying, took me years.
Camera bags: Again Ken Rockwell has great advice, ThinkTank pro camera bags if you want to spend money, a kids diper bag, cloth grocery sack, or whatever is comfortable and blends in if you don't want people to know you are carrying $5-20k in camera gear. If your favorite bag lacks padding, a t-shirt is enough.
Straps: if the one that comes with it isn't comfortable, there are a zillion padded ones out there with all kinds of buckles and slides. Some people like to replace flashy camera logo straps with plain ones. The only thing I would watch out for is a rubbery foam strap that lacks a tougher layer it is sewn to. I had a rifle strap break while hiking, and realized it was just a strip of neoprene.
Filters: Hoya HMC triple coated. Very expensive and hard to clean. But I found dirty filters rarely effects photos. If you are out in the field and you filter is too dirty, you can just take it off for a shot. The expensive coatings take out the lens flares, cheap filters add a few more flares. I try to always have a filter on, I have broken several dropping cameras and they protected the lens from damage.
Sunshades on lenses: There are almost no situations where they block the sun from causing lens flares. You can use your hand or hat on those occasions. They offer a bit of scratch&bump protection, at the cost of another bulky fiddly bit. Not worth it for me.
Tripods: I never could justify the expense of solid, lightweight, easy to adjust tripods. You can easily spend $1000+ on a good tripod setup, and its absolutely worth it for some photographers. I went with a flimsy light tripod that is mostly plastic, and a heavy one with a dozen thumb screws and just worked within those limitations.
Software: gimp.org is the standard free photo editor, does great, works on slow computers. Faststone image viewer is the best photo viewer/sorter, its free but only on Windows.
Its easy to for people of a certain type to become gearheads, I lost count of how many cameras and lenses I have once I got into film and old people started giving me their unused cameras. Obsessing over the technical details can get in the way of getting out there and finding interesting places and situations. Getting used to your lenses and the lighting conditions / focal ranges they work best in will have more results than someone with better gear and less experience. At the end of the day its about looking at a scene and knowing how the camera will see it, not how you see it. Just takes practice and that artistic spark of perseverance towards an inner vision.