For the location of the connection:
You want the location of the hole to be at the balance point between moment caused by the centrifugal force outward and gravity downward about the center of gravity. There are many ways to make this perfect depending on the speed of which you rock/swing the wand/cane. The faster you spin, the closer to the center away from and the slow you spin, the further away from center. For a beginner, I have found that 1 inch above a perfectly balanced 30” wand/cane to be the best. This will change depending on whether or not you have weight on top or bottom. I prefer to use a slightly bottom heavy wand/cane and then place the center ~2.5% of the length.
For your 895mm, I’d say place the hole 20 to 24 mm above the balance point.
Now for the harder part, the length of your loop:
Beginner Flow wands: Hand span past half length. Close enough to stall but long enough to get around.
Magician's cane: Looped (no knots) at 3/4 length to facilitate certain two handed levitations.
Long string is considered anything past 1 full wand/cane/staff length, usually 30 inches or 75 cm.
Loopers/Hoopers or ambidextrous passers will make theirs a little less than wing span but never use the full length.
Double wand (Linked) length is your height if you pass it behind you (magicians) and your height minus your shoulders if you are a front passer (spinners).
The longest I'd recommend (usually rope dart and hammer spinners) is about 1.5 your arm lengths, unless you are very quick at hand wraps.
Other considerations:
Decoration – Make sure you use something bright to catch people’s eyes a hoop glitter tape works well.
String – Definitely Kevlar thread if you are using a fire ward. Coats and Clark Dual duty for most applications and their 0.004” black nylon if you are a magician.
Weight – Your dowel will work well for now, but considering air drag, a slightly tip heavy (more rotational inertia without a lot more weight) tends to work better for keeping your wand/cane perfectly upright.
Rods vs Tubes. – tubes are lighter for the width of wand, they can hold much, much more fuel, and can hide the string inside when used just as a baton.
That’s all I can think of for now. Good Luck!