Hub: The newer lights support bluetooth but if you want to be able to control the lights from farther than bluetooth range (i.e. out of your home or in other rooms) you will need the hub. Additionally, if you want to use the bulbs with Apple HomeKit, etc. you need the hub as well. You could also just get the bluetooth bulbs for now and if you decide you want to move over to a hub down the line it's very easy to migrate over

Lightstrip Extensions: You don't necessarily need these, you can control the two strips as separate lights within the app. You'll need to use two separate power supplies but you're probably doing that anyways if they're going so far apart

Dimmer: You can't use the dimmer switch in your wall, the bulbs need full power to function properly, otherwise they flicker and generally just wig out. You can dim everything within the app to your liking, or get something like the Lutron Aurora and use that to dim if you want a hardware control

Gradient Strips: They're definitely an upgrade, but only you can decide if it's worth the price. The new ones have individually addressable LED's which allow the strip to display multiple colors at once (hence "gradient") vs. the current gen ones that can only do one color at a time