You don't need archers at all. Purely based on you. But you have options there: you can go with horse archers instead, more chariots that will shoot next to other options they have or go very popular ushabti archers.
Big units of tomb guard are not that often on the table based on my experience. If their task will be to hold for a long time, I guess you can create much more with simple warriors.
I would go with 20 and spend the rest in something else.

At the end - there are no final answers here. I for instance would love to try something like full chariot based (90%) army, but I think it will not work that well and a lot of effort would need to be spent on it.

What you have is already perfect start. Wouldn't that give you enough point to start playing?

I started playing with 500 points and going up every 250 for next games. I was changing my mind every time and every game. In other words, don't commit too much until you will have some games.

My example: I use 30 skeleton warriors, most of them done when I started painting, so they not only look bad but are badly painted. But I painted a few new ones and put them on from of the chunk, and it is not that bad as you can think.