I've also made rhubarb wine in the past, using a recipe from a very old wine making book* which generally veered towards adding too much sugar (to my taste, anyway). I don't think rhubarb has very much sugar at all, so you will have to add plenty.
I found my old recipes (2005-6), they vary a bit, but it's clear I had access to a LOT of rhubarb. For a 7 gallon recipe I used 30lbs rhubarb, 5.5kg sugar. I recall it being a pretty dry result, fermented to 10.3%, and really was a rhubarb flavour wine in a light pink colour. As far as "mashing" was concerned I used to chop the rhubarb, pour over boiling water and leave for a couple of days (or a week in one case). Sometimes I used a pectolitic enzyme, sometimes not, it didn't appear to make much difference. I also used a press to extract all of the juice once I'd steeped the rhubarb, which was a messy experience, but seemed to retain a lot of the flavour.
Looks like all of my recipes were roughly similar, 1Kg of sugar / 5lbs of rhubarb (I know, mixed units, but the sugar comes in Kg bags....), but of course you can adjust depending on how strong you want the final result to be. I don't think aiming for stronger made it better, and my preference is for a dry wine anyway, so I'd aim a bit lower and let it ferment to dryness.
Most of the older recipes went on to say "use it to mix with something else", but I loved the taste of it on its on. Shame I don't have access to the quantities of rhubarb I used to. It was growing wild on an allotment I had, and the Champagne variety quickly grew too big to eat, but was great for wine.
Oh, and finally, I never bottled until the year following the harvest, although I'm sure I racked a couple of times between demijohns...
Enjoy!
*Probably "First Steps in Winemaking" by C J J Berry