I've done star trails with an X-T2 both with a wired remote and with the intervalometer.
The in built intervalometer does work well, but if you are a pixel peeper (there's a lot on here

) you might find that you can just spot the gaps in the shots. Don't know what software you use but I'm on Star Stax. Using a wired remote locked into continuous shooting gives no discernible gaps. It seems to take the intervalometer a second or two to change over between shots. It really depends how fussy you are.
This was taken with the intervalometer and you can see gaps in the trails. (Of course it may be something else causing the gaps!)

Ribblehead by
Frank Yates2010, on Flickr
whereas this was taken with a wired remote and there doesn't appear to be the same problem.

Formby Point by
Frank Yates2010, on Flickr
The L bracket question is a tricky one. If you use the camera in landscape mode then you should have no problems regardless of using the mic socket or the micro USB post. Both will fit in but both are a bit awkward to either insert or remove. There's not a lot of space for your fingers! Some brackets have a cut out on the upward piece to help with this.
The real problem arises if you use your L bracket in portrait mode. The you have the very real problem of where to put the cables. A genuine Fuji remote is of little use. There is a big ballast resistor near to the socket and this just won't allow you to use portrait mode at all. I'm using an old Canon RS60-E3 plugged into the mic socket. This has a very shallow 90 degree connector. It will allow use in portrait mode but it is a very tight squeeze and you have to be a little bit "forceful". The connector fits OK but the little door gets in the way. I adapted my L plate to give double clearance so that problem doesn't recur, but you need to be a bit creative and practical to do that!
I'm assuming that you will be using the £20/30 brackets from everyone's favourite auction site. You can completely get round the question of use in portrait mode by buying the Kirk or RRS brackets. These come with a sliding bottom section so allowing you to increase the gap between the camera and the top of the tripod. It solves the problem, but you may have to recompose if switching between landscape and portrait modes. Plus there's the extended bracket that you have to remember to slide back into place after use. These are reputedly good stuff, but at prices of approx £200 last time I looked they don't come cheap.