Yeah I see the recipe uses a lot of white pepper and higher fat content which is in line with my experience.
1) Curing salt, as many of the more experienced guys will tell you, is one of the more important ingredients (people vary on opinion but generally its better to include it if you aren't sure). This is not something want to get wrong so if you are unsure what curing salt (not sodium chloride) you have, I would rather bin it and buy a new bag of something labelled. In South Africa, we get Prague Powder #1 or #2 which is referring to whether the curing salt contains (in addition to sodium chloride) sodium nitrite or a combination of sodium nitrite and sodium nitrate. You will find a lot of info on this forum as to what ratio of curing salt to meat should be used.
2) I prefer to let the meat sit overnight. It's all about flavour equilibrium
Maybe the more experienced guys can chip in here with their experiences? Go ahead and fry up small portions it will give you an idea. I actually ended up just frying small patties of one batch since I couldn't wait for them to be piped
3) Not that I've run across. I've tended to make smaller batches (1kg each) with different spice ratios to see what is best for me. It does help I have a gram scale for measuring acurately but you can get those cheaply.
Hope that helps.