1. Timing can start when you hit the switch since your machine does not have preinfusion. Depending on the machine the 1st drip may be anywhere between 1-20 secs. You can brew 25secs and then grind finer and brew something at 35secs achieving the same brew weight and see how it tastes.
2. It could be the coffee is preground or light roasted or you are using a pressurised portafilter and the grounds are not fine enough.
3. pressurised portafilter is the way to go if you are using preground. Preground will lose freshness rapidly and if you use nonpressurised portafilter with preground you will see your flow rate get faster and faster as the coffee continues to lose its freshness.
4. Yes. a finer grind will result in lower flow rate and hence a longer extraction time (Assuming you maintain the same brew weight).
5. Material only matters in its durability. 15kg is just a rough gauge. you can use a calibrated tamper or just tamp without overexerting yourself. tamping does affect the flow rate but not so much unless the barista is wildly inconsistent between using feather light tamps and gorilla tamps.
6. Not familiar with opv mod or steam wand mod. But a classic steam wand (and the necessary skills) will definitely get you better frothed milk than a pannarello.
Thanks!
For the calibrated tamper, should I be getting 57.5mm or 58mm if my portafilter is 58mm? Understand that tamper is usually slightly smaller than the portafilter, correct?
On the extraction time, 25s ends when when the color turns lighter brown yes?