Oh, boy, are you in for a treat. Yes, it can be done like that, and it will work, but if you want repeatable recipes, measuring is useful. This need not be hard, nor expensive. Cheap 10ml syringes from the drug store or pet store or farm store or online work well for measuring. Juice calculators are free--
here's the one I use-- and handy for remembering what you did last time since you can save them. Empty juice bottles work well for storing your treasure, but glass, dropper top Boston Rounds work better, are available in larger sizes, and last longer. Not too expensive on eBay. You may or may not want a sweetener. I use some in practically all my juices. I, myself, use borosilicate lab glass for mixing and measuring, and I'm considering building a powered stirrer to make the job easier. But I also mix in pretty big quantities, too-- 500-1000ml, usually-- so you might not need the extra stuff. You can get by with a few syringes, a coffee cup and stainless spoon for stirring, and some old juice bottles.