Okay, you're going in the right direction. You've already got a low seat and now the X-bushing will drop it about another inch. How much you need to drop the front to compensate is a personal preference. I dropped the front on my GF's bike about 3/4 of an inch to compensate, and it works great but it's an older RFS KTM with open chamber forks. Here's an old article on the X-bushing for reference.
Synergy Seals X-Bushing - Dirt Rider Magazine | Dirt Rider
You'll have to experiment with what works for you, just be sure and lower it less than the point the tire makes contact. As FE350 says, the 4CS forks are super-sensitive to height changes as I found when I played with the front end height on my TE300. Handling gets more unpredictable if you lower it IMO. You're results might be different, especially since it's a different bike, and with the X-link you will need to find the set up that suits you.
I also think a lower rear tire can reduce your seat height a noticeable amount and yes it will change the geometry a bit and might or might not affect handling in a positive or negative manner. This may require you to adjust youre set up to compensate.(The difference in front tire sizes are negligible IMO) The 110/100-18 on my TE300 is roughly 1 3/4" inches taller than say a 110/80-18 Pirelli MT21, which would lower the rear almost another inch, or at least 1/2 of 1.75".
https://www.rbracing-rsr.com/tirediamcalc.html
The professionals at suspension shops use spaces to lower, which is the "proper" way, but will reduce travel and still require you to set up their changes to you liking.