Your tall fescue seed is coming in nicely. Definitely do not use fire to kill out the weeds it will kill the grass seedlings as well.
As soon as you mow the new grass a couple of times, you can safely apply WeedBGon and knock out those winter annuals.
At the time of spraying for weeds, fertilize the tall fescue again to crowd out future weeds. Tall fescue is one of the best weed preventers when it is maintained properly due to its thick, dense nature.
Where are you located?