You keep referring to L298N which is a chip, but your picture seems to show a module containing an L298N chip and other components. This is what I was asking back in reply #3, but you still haven't provided any more details or a link. If this is what I suspect, it may have a built-in 5V regulator which could be used to power the Wemos.
True, L298N is not very efficient, and it's built-in regulator won't be either, so not recommended for projects with small batteries, but you seem to be planning to use a reasonably large SLA battery, so while not ideal, it should be ok I think, at least for now. If you find later that you need more battery life, then you can start worrying about more efficient motor drivers and buck converters.
My next concern is: will the 3.3V signals from the Wemos be able to drive the L298N?
EDIT: According to page 3 of the L298 data sheet, any voltage over 2.3V should be recognised as a HIGH input, so the 3.3V from the Wemos pins is no problem.
However, with the max6675, if you power that with 5V, it would need at least 0.7*5=3.5V HIGH signal, so the 3.3V Wemos pins would not be high enough. Fortunately, it looks like you can power the max6675 with 3.3V from the Wemos' 3V3 pin, and again no problem.