My recipe from my mum is very simple. I dont recall her making pickles very often, so I have pushed the practice)
Beats me why professionals cant do it better

I like "Malt vinegar" taste.. and I think it is needed for onions?
For Gherkins/dill pickles I use WHITE vinegar and just DILL as the spice. Never tried with garlic... doesn't appeal

Piccalilli involves adding veg to hot "sauce mix" and I do sterilize jars since a large batch lasts maybe months.
But for gherkins, red cabbage, onions there is no cooking of vegetables, and just clean jars is sterile enough.
The basic process for onions is to peel onions and soak in brine (salt water) overnight.
Then pack in cold jar and fill jar with spiced vinegar.
Leave several days, a week or so before ready to eat.
To make spiced vinegar:Per litre (2.1 US pints) of malt vinegar.. add 1/2 cup white sugar (you can vary amount of sugar to taste but the effect is supposed to be a balance of sweet, spice and acid), and generous amount of WHOLE "pickling spice" bring to boil and simmer 10 mins. Let it cool in saucepan.. then strain through fine sieve to get rid of spice bits. I make the spice vinegar after peeling onions, and so it is cold by time the onions have been left in brine overnight, and I use the spiced vinegar next day.
Whole Pickling spice mix may vary...
Main spice is cloves. I add extra cloves if the mix looks a bit short of cloves. There is generally coriander seeds, yellow mustard seeds, black mustard seed, dried ginger, cinnamon, whole black pepper corns, allspice berries. I remove most of dried chili bits.. I don't mind chili but searing spice heat is NOT what pickled onions need.