Hello! actual wheelchair user into historical fashion here!!! we don't have *much* overlap since i prefer skirts and dresses however i can still give a few tips!
having things sit or end at the waist is good advice, it make the silhouette nicer and importantly: does not put the bulk on your hips. Generally, i like to avoid bulk or seams at my hips because I've found that gets painful fast, and makes it hard to sit!
Additionally, if you sew for yourself, and you haven't done so already: Retake your measurements while sitting!!!!! I know i have to add a few inches to my waist and subtract a few from my inseam so that they look nice whil I'm in my chair. keep in mind your thighs will also be more compressed!
If you have a manual wheelchair, make certain to keep anything within two or three inches of your wrists well-fitted, especially to avoid them puffying out and getting Wheel Gunk on them.
Also, I would invest in things to secure clothing. Somehow, I find my clothes frequently need re-adjusted, and when your hands (or hand, for electric) is what keeps you moving... having to stop to re-adjust clothes can get frustrating! So, pins, clasps, ect!
If you do not have a tie-on pocket, I found making myself one was a very smart idea. Bernadette Banner has a video on making them, but I adjusted the pattern to be smaller, because again, bulk can quickly become Too Much when in a chair. The reason this pocket is a life saver is because I've found many pockets sit too high up close to my hip joint and too far to the side to be properly useful, because i just Cannot get my hands in, nor can I actually Store things in there. but a tie on pocket can be tied at the waist and shifted to sit further towards the front of my body!
Furthermore, here's something fun: no one will ever see the back of your waistband ever again. if something has pleats you need to take out, take them out from the back first, and you won't need to redo them because no one will see (and also pleats hurt to sit on).
Agreeing with Vincent that decorations along the front of pants will look very snazzy!!! side could be nice, but isn't as likely to be visible, though it varies person to person!
And, for any modern fashion you may or may not wear: i find shorter pants/trousers tend to look best if they hit at or below the knee. Especially if you have belly fat (not a bad thing!!!!!!) , your tummy will cover will cover the top few inches of your thighs making things look much shorter, and also you just don't wanna flash people from the front.
Another good thing for manual wheelchairs is you'll want to make certain you have flexibikity in your shoulder and upper arm, so ensuring you have a good fit on your arm scye is a must!!
also... depending on your height, avoid super tall hats (i.e. stovepipes.) people will be viewing you top-down, so a medium or short length hat might work best!!
also: Congratulations on the chair!!! I hope it serves you well for many years to come, and that you teo get to go on many amazing adventures together!!!!!
now, i believe i need to make myself a capelet for winter...