You have the right idea with the button and joystick, and I can expand a bit on some tips:
1. For crops - your best bet for placing crops is long rows where you use the joystick to run and just press the button as many times as possible, then turn around. With invisible buttons you can even do something called 'butterfly' clicking (clicking the button with two fingers back and forth quite fast), to place fast enough that you don't miss any spots
2. You can also use the visible buttons and joystick settings and click both of the buttons in succession when planting which should work
Kegs (and any machine you have to refill), really suck on mobile, I generally recommend using something like pigs or honey instead (I have a honey farm and video guide which is aimed at being as easy to use for mobile/console here on the forums).
If you do want to use kegs:
1. You want to be filling them vertically, otherwise they're incredibly frustrating to deal with (you'll see how I try to use this the most if you look at my honey guide)
2. You want to empty them then fill them, it's slower dealing with trying to empty and fill at the same time then just running through everything twice
3. You want to use ancient fruit, then you don't get the annoying eating popup every time you don't click perfectly. You can still use other crops but you definitely have to be using tip 2 if you are.
4. Place off farm. I recommend this in general but on mobile it's especially relevant. sheds aren't really designed for placing vertically so you waste a lot of space and still have to turn around a lot. Areas like the quarry are amazing, you just cover it all with some paths so the rocks don't annoy you and you have a lot of quality vertical space (enough for about 500 machines). Other places that are good are the right side of the train tracks, ginger island west, especially the desert, and some places like the backwoods are decent too.
Feel free to ask any questions, I have a fair bit of experience on mobile so I've collected a lot of little tips here and there