No, you can't just have a single anchor point. If the dowel isn't anchored at each end, it will pivot or rotate at the centre and be a real nuisance. So whether you have solid braces or chains hanging from the ceiling, there needs to be one at each end of the dowel for stability.
How long the braces/chain are is dependent upon how high your ceiling is and how tall you are. If you don't want to mount something permanently to your ceiling you might check Kati Meek's book Dance with your Loom for how you can mount an apparatus to your loom by clamping it in place. You then need to remove it after each time you dress the loom but.... She calls the device a warping trapeze. I learned of this tool in Sweden (prior to Kati's book being published) and it was translated into English as a 'warping valet' so that's the name I learned for it. :)
As for how I attach the weights, I don't use a chain but a loop of string. 4/8 cotton - not rug warp, but a softer spun yarn that is a bit 'grabby'. The loop goes around the warp chain, pull the knot through the loop and attach an 'S' hook to the loop. The water jug also has a cord attached to it with two loops, one near the jug, one about 1.5 yards away.
To begin with I use the loop nearest the jug. When the warp is almost beamed, I use the loop furthest away from the jug so that the long cord will go up and over the valet so that I can beam the warp almost it's entire length using the valet.
When the warp and cord are too short, I take it off the valet and then hang the weight off the warp over the breast beam for the final couple of feet.
I'm sorry, but I didn't understand the question about the warp lease. Email me with more details and I'll try to answer. laura at laurafry dot com
Check the label 'warping valet' as I've posted about using this tool quite often. Or check my You Tube channel as I have at least one video clip showing the beaming using the valet. User name lauraannfry1