Soak the chillies in brine first then pickle in vinegar. Do NOT use malt vinegar - it's fine for onions but too strong for chillies. I'd go for cider vinegar myself. Make up your own spicing or leave it out altogether. Do NOT preserve in oil unless you have a reliable, detailed recipe that also includes vinegar.
Chillies have virtually no acidity and without acidity various very dangerous bugs can grow.
My final suggestion is to spike your favourite chutney recipe with your chillies. If your chillies go red then you could try my plum and chilli sauce . I have never heard of it. Panch phoran is a Bengali mixture of 5 spices. Chilli Willie's Spices by Post sell them all.