I am lifting Sundays, Mondays, Wednesdays, and Fridays. So far I have worked out like this:

Past Sunday: Chest, Back
Monday: Biceps, Triceps
Wednesday: Shoulders, Legs
Friday: Chest, Biceps

So my question is, what would be the best way to cycle with lifting these four days a week? Just keep switching it around? Like tomorrow on Sunday could I do Back and Triceps? Unfortunately, that would leave Shoulders and Legs on the same day together again so wouldn't you want to switch it around to have different body parts on different days? If you do that you risk just doing a body part once a week if you forget to make sure it's done twice

With the same two body parts every day four times a week you know you are getting each body part two times a week but is it bad to do say chest with back every single time?

Is it ok to workout Shoulders and Triceps the same days?

Just trying to figure out the best way to do this with my four days a week and with these muscle groups.