1) I would say: Making these bread rolls I didn’t have any kitchen scale at hand, to check the necessary ingredients, so I just did it "by guesswork". -I don't think you can use the word eyeball in this context: you can "eyeball someone" - or look at them very closely. -You could "eyeball a restaurant menu" to decide which items you wanted, - But, I don't think you can use eyeball to refer to evaluating the weight of ingredients in a recipe: i.e. guessing the approximate weight. 2) I would say: I planned to do a lot of things, but woke up with a terrible pain in my back. Then I understood that (all) my big plans were (or: "had gone") up the spout.

Yes on number 1. Number 2 - you have probably understood correctly, but I have never heard that expression in almost 60 years.

Your meaning of eyeball is correct, but your use of it isn’t quite. You would ‘eyeball’ an amount not the ingredients themselves. I hope these taste OK - I eyeballed the amounts when mixing the dough. If you don’t have a measuring cup, just eyeball it. (Estimate the amounts) How many people are there? I don’t know. I’ll start counting. Don’t do that. Just give me an eyeball estimate. I’ve never heard of the other expression.