I eat a lot of soup! Therefore, consume a lot of salt.. Sometimes up to 2,500mg a day, but usually less than 2,000mg..
Can this seriously interfere with my weight loss or just make me hold water on the scale?
Same with caffeine. I don't drink soda or anything with caffeine in it lately, except my morning cup of coffee. (generally about a size medium, which I drink throughout the day, nursing it, not gulped down at one time)
How does this affect my weight loss?

Yes it can because salt makes you swollen and it also can make you dehydrated which can interfere with you trying to loose weight. Coffee which has a lot of caffeine also interferes with weight loss because it does the same, dehydrates your body. so if your going to eat soup and drink coffee, I would drinks tons of water and it will help if your trying to loose weight.

To much salt makes you retain water as does to much coffee. However, coffee supresses your appetite a bit which is why most diets allow you to have dark coffee.

salt makes you retain water try taking a water pill
caffeine makes you feel hungry