How can I improve my cable routing
You want to get the housings situated closer to the frame so there's room to put your bag in front.
They curve pretty far into that space now. To get them as tucked as possible:

Don't zip tie them together like that.
If your STI model is one that has two routing options for the shift housings, use the one that puts them behind the bar.
You can route the brake housings (as well as the shift if the above option doesn't exist) so that under the tape they slope downward, and then exit around the 6 o'clock position on the bar, rather than in front like they do now.
Make them all as short as possible. They don't look like they are now. This is usually defined as the minimum length to still have some slack when the bars are turned as far as they're able in either direction.
Corroborate that you can't cross the shift cables under the downtube (usually not possible with this style and location of stops). If you can, doing it that way may make the housings protrude less.

The bag you have isn't made to work with a handlebar bag rack and decaleur, but eliminating this kind of problem is one of the things they do, along with the sorts of handlebar bags they're used with. They could also provide a better place to mount the light as well.
For the light, if the above doesn't get the housing out of the way, one avenue is switch to metal fenders, use a bracket to get the light all the way forward on them, and put an additional strut behind it for stability. A number of old and new rando bikes have this sort of thing. There's even now an off the shelf product that does it. Do not forego the additional stabilization of either a strut or a rack, and don't do it with plastic fenders.