I'll second the advice above more explicitly: keep the Hue Bridge. 
At the end of Hubitat's Zigbee mesh tips documentation (or a search of this forum and some others), you can see that many bulbs behave poorly when mixed with other types of Zigbee devices (which you have: your ST motion and multipurpose sensors). Keeping them on their own network, like a Hue Bridge, keeps all your devices happier. It works more or less the same as ST, where you must currently also be using their Hue Bridge integration (Hubitat has one; I wrote one myself, too, with a few extra features).
LIFX doesn't have an official integration, but there is a community integration that works well for many people. Everything else looks like it should be pretty easy to move. If that's an exhaustive list of all of your devices, I might suggest adding at least one repeater. All of those sensors are Zigbee and might benefit from at least a Zigbee smart plug or other repeater (the Ikea Tradfri outlet is cheap, the Ikea USB repeater is not much more but a lot smaller in size and arguably prettier, and there are a ton of other options like the SmartThings 2018 Zigbee outlet). For more than 32 Zigbee devices, you'll need a repeater (same as ST v1 and v2 hubs), but it's a good idea regardless, especially since some people report that Hubitat's radios don't seem to have quite the range as ST's.
You don't have a ton of devices, so if t were me, I'd probably just remove everything from ST and pair it to Hubitat. You could jsut reset the devices and pair them to Hubitat without "politely" removing from ST if you want to reference ST for automations (in case you forget how you used the devices). But I understand it may take some time to set up your automations and everything in Hubitat the way you like it, to say nothing of whatever adjustments you may need to make to get used to the new platform. Hub Link and HubConnect are two options you can use to "share" devices between platforms and ease the transition, but if I only had 15 sensors, I probably wouldn't bother. You could transition slowly from one to the other (in many cases, destroying one mesh as you build the other can be an issue, but again you didn't specify having any repeaters, so this doesn't matter as much--though I'd be careful not to put ST and Hubitat on the same channel while you're moving).
