The first episode is scheduled to air today (4th October), but it's not unknown for them to advertise the start time as "25.00" i.e. really 1am the next morning. So yes, it begins in Japan some time within the next 24 hours. Then we'll have to wait and see if any of the fansub groups take it on.
The TV show is a prequel about Jinga. Going by the trailer I'm guessing that it's about how he gradually became consumed by a Horror. No sign of golden knights in it thus far.
From what I saw online, Jinga was pretty well received when he shows up in Gold Storm. You'd think a campy, hammy villain would be out of place in Garo but really it made for a nice change of pace and he's way more charismatic than the usual 'silent, half-naked, giant woman' final bosses.
Personally I wasn't keen on Red Requiem, but it's been years since I saw it so maybe I'd think differently if I saw it again. I get the impression that the general rule with that film is that people who had already seen the first series didn't like it so much but people who had never seen Garo before did enjoy it. It was meant to be a jumping on point before the second season because at that point there had been no Garo for three years.