Off a 53.7 400m and an xc base, I'd say that your 100m is probably going to be in the low 12s. Possibly 11.9x if you've got good acceleration, but not too much faster than that. For what it's worth though, 100m, 200m, and 400m times can line up weirdly. I've known guys that would win 100 and 400 races against others then lose the 200 against the same guys that they beat in both the 100 and the 400. I recommend simply racing the 100 a couple times, and seeing how you do. However, I would assume 11.9 - 12.3.
Depends how much speed endurance you have.Usually your 100m time is 1/2 your 200m time(usain bolts 19.19 200m is close to his 9.58 100m(19.19/2= 9.595) So your 100m should be 12.1ish IF YOU ARE IN GREAT SHAPE. if not, your 100m time will be less than half your 200m( since if you aren't in good shape, it's harder to maintain speed) so you can expect a 100m ranging from 11.6-12.2
