If you are using RC components...which I don't suggest at all, then get a Castle Creations ESC that runs at 12S max. They use decent mosfets and will do what you need reliably. Cheap RC stuff is NOT going to hold up at all...just don't waste your money on them. Also, 6S might sound OK for now, but trust me...it won't be long before you'll want more performance. Just plan for being able to use 12S from the get go. Personally, 48 volts isn't enough IMHO. My low voltage EV runs at 66 volts and does 43mph. Everything else runs at 82 volts or higher. Do yourself a favor and plan ahead for more than 6S.
What kick scooter did you have in mind to base your EV on? I've looked at quite a few and some have more potential than others.
Since you are standing up, a thumb throttle is your best choice. Twist throttles require holding onto a twisting grip and standing up. What you want is your hands planted on the handle bars as much as possible. I've built 2 stand up kick scooters. See the links to them in my signature. I originally used a twist throttle and when I discovered thumb throttles, I never looked back. If you are seated, then a twist throttle is fine. For standing up maximizing stability is your best friend.
Motor KV/RPM is going to possibly get you in trouble. A high Kv motor is going to spin really fast and that means high gearing ratios. If you are doing belt or chain, it's still the exact same issue for gearing. Hi Kv motors work great for small diameter wheels like on a skate board since the motor spins fast and the wheels spin fast too. Any adult sized kick scooter is going to have wheels that are 8" in diameter or so and maybe lots larger. They are going to spin much slower than a skate board at the same speed. The bigger the wheel the slower it spins at the same speed. That means a fast motor needs to be geared down a LOT to get it to drive a large wheel at realistic speeds. You would do better to get a much lower Kv motor so that gearing it down for your kick scooter is less of a problem.
Belt vs chain...
Belt is quiet...really quiet. Depending on the chain option, some is noisier than others. You pretty much have 3 options that will work for whatever you are doing. Bike chain, T8F and 219. For inexpensive EV's, T8f is commonly used. It doesn't come in very many sprocket sizes and you pretty much are going to China/ebay to get it. I started on T8f and it worked well enough for me at first. Bike chain and components are almost always designed for use on bike freewheel threads or bike cartridges. I don't know of anyone that makes motor sprockets that fit bike chain. So then 219...it's strong and probably overkill for your needs. However, I use it exclusively and I can tell you it is really good stuff. Sprockets are readily available in lots of sizes and it's not very expensive. Motor sprockets come in lots of sizes.
Motors...I like Alien Power outrunners. They are generally built with EV use in mind and that means beefier bearings and larger motor shafts and optional halls. Most RC motors are not really intended for EV use and they need to be tougher in order to haul you around.
Any servo controller will work with any RC ESC. With a little adaptation, it can be ran with a hall throttle. Honestly though...ignore anything in RC components and get a real EV grade controller and throttle. It's a far better choice, handles over load conditions better and works directly with a hall throttle.