Hi Lou,
the approach i use for filling in the crack/crevises is wood glue and sawdust. first its easy to sand and second, its a bit easier in my view to get a color match.
a thin crack i wil lay in some wood glue (tip cut with a pin point into the crevesse)…then i will push the sawdust into it using the sawdust of the color of the strip i am trying to match. i will let it set up for a bit then use 60 grit sanding block. bigger cracks may take an additional pass or two.
as mentioned, i find it easier to get color match then epoxy. also no mixing, just easier in my view. you can also do little bits of work at a time. epoxy is tough to mix in small batches and then you are either wasting a lot or trying to move too quick as you are working around epoxy cure times.
based on you pictures, i think you are doing fine for a first strip built. experiment with the technique i am suggesting. its inexpensive to experiment with wood glue and saw dust.
on your second question, you can go either order. i ussually will start with fairing becuase is can be hard to cut recesses properly on a rough surface. but once i cut the recess i typically still have some final fairing to complete the fairing work.
here is a link to a previous forum string on the same topic dust + water + glue mixture to fill gaps
h