Anyways, regarding parts.
A lot of people don't like the stock Hori joystick or buttons.
Hori Real Arcade Pro 4 Kai (what a mouthful, eh?) comes with Hori's own stock joystick called the Hayabusa as well their own company made buttons (also called Hayabusa). Thing is, their buttons and stick are controversial and not well liked. Hayabusa buttons imo are the worst buttons on the market.
Pros benefits of various stick parts:
Joysticks
Hori
Info: The Hori Hayabusa. Sensitive as fuck. Very loose and light which requires pitch perfect execution. I hate this stick in stock. I added a spring mod to it. The stock stick has a very, very light spring which makes it feel like you're maneuvering a feather. I put in a 1.5 pound spring in mine and everyone I know, including me, who has used that stick since has loved it. Here's the deal with Hayabusa stick. Stock, people mostly hate it but it has its audience. Personally, I find it too loose to execute in stock form and this hampered my ability to grow as a player. Modded, it's a top tier stick on par with or better than Sanwa. It's also an easy mod (considering). Just need to put a 1.5 lb spring and take out its stock spring. One cool thing about Hayabusa is how when you move it makes a click as you rotate the stick. This can be good or bad depending on if you're playing at night, but it feels so mechanical and feels good. Combined with a spring mod and you've got yourself a good stick.
Sanwa
Info: Whew. This is what we call the JLF. This is the standard. It's loose but it has far more weight to it than the Hayabusa. It feels nothing like a modded Hayabusa but it feels precise and exact while still having a little looseness to it. Highly recommended if you don't want to mod your Hayabusa and want an alternative to the stock stick.
Buttons
Everyone's favorite topic. Mother fucking buttons.
Give me some air, boys and girls.
Hori
info: Hori's buttons are also called Hayabusa's. They're matte. They have a blah plunger. It doesn't have that smooth click, mechanical feeling. These buttons are WACK. I know very few people who like these. All of us with Hori sticks have replaced them shits with Sanwa or Seimitsu. These are TERRIBLE. Their best positive is that they are responsive.
Sanwa
Info: OBSF-30's. The GOD. THE arcade standard. They got that fucking smooth finish. They feel good to press. When they go down they go into the plunger and it FEELS. GOOD. I cannot explain it. They make a click when you press them. I am biased here because my loyalty to Sanwa's buttons is that fucking serious. These buttons are ones with a light touch. If you touch them they WILL respond. This means you can't mash shit or rest your fingers on them much but at the same time this allows for really precise execution techniques, like piano, negative edge, double finger-ing for a mash move or just doing good ol' combos. They're responsive and easy when doing things like combo links and make it easy to glide your finger from button to button. I. Love. These. Buttons. These are standard for a reason.
Seimitsu
Info:
Seimitsu PS-14-GN's.These are the polar opposite of Sanwa's line and just as viable. I really like these but not the way I do OBSF's. Notice that they have a flat top. These are the opposite of OBSF's in that they take a bit more to press the plunger into the actuator. Meaning they're not light and are more mechanical. For those who like a more hard touch and like mashing their buttons or resting their fingers, these are a better sell than Sanwa and have their own audience.
IMO? Get an 8 pack of Sanwa OBSF's and an 8 pack of Seimitsu PS-14-GN's. They'll cost 20 bucks a pop but you'll get to see which you prefer. Buttons are easy to install too. Just unplug and plop em out/in. Alternatively, make a choice now and then get the others later. Or maybe you'll be fine with the stock Hayabusa parts (yuck). Who knows.
Stick vs Pad
What Prof. Beef said about not needing stick is true. But it's also kind of wrong. If you go to any local fighting game hang out, we have some stations with sticks already plugged in. A lot of times people bring their own sticks for people to play on and it might be on a system that does not take your controller, like Dreamcast for instance. Or NeoGeo. You'll be dealing with what people bring. And you don't know how to play stick? You're shit out of luck. One time when I was a pad player, I forgot my pad at home. I swear I brought it.You know what happened that night? I couldn't play worth a damn because I couldn't use stick. The local had loan me sticks and I took one but I couldn't use it. If I could use stick, leaving my own stick at home wouldn't be a problem because I could just ask a friend if I could use theirs. I decided then I'd buy a stick. Why? To just learn how to use one. One benefit of learning stick is that you can play on any stick (even ones with awful parts) and since that's the fighting game standard, you'll be able to go to arcades while on a trip to Japan and play no problem. Good luck with that if you're a pad player. They sometimes bring arcade cabs to major tournaments. If you want to play on that cab but can't because you're a pad player? GJ. Being a pad player in the fgc only limited me. So for that reason I suggest at least learning how to use stick. A player like Punk plays competitively on pad, but still knows how to use stick. There's preferences, and then there's practicality. No harm in using pad to play fgs. Many players do so. But at least get a stick and learn how to use it so that when you're at a fun event you're not left out because you decided to not learn to play stick.