You’ll need to use glass paints so the heat will not destroy the paint as you fire them in the oven first once you’ve painted them.
You use the extra long matches to light the tea light or you’ll scorch your fingers if the jar in too deep and/or narrow.
I make my own for the house at Christmas Time.
Also you can make candle in the jars so the wick is at the top of the jar.
And yes I soak jars in hot soapy water and give them a good scrub rinse and leave to dry then into the oven to sterilize them. I put mine onto trays as it’s easier to get them in and out again.
I leave them in the oven for about 10 minutes after I turn it off just incase the sudden drop in tempeture fractures the jar.
I use this method both for my candle jars tea light jars and for making preserves.
If you want to bring the tea light up you can provide little bags of coloured sand to place into the botton of the jar so the tea light comes up a bit closure to the top of the jar and the colours looks pretty.
I sometime buy floating candles and pour water into the jar about halfway with some coloured beads or flower arranging coloured glass pebbles at the botton and the overall effect is so pretty.
I’ve even put tiny springs of holly into the water in the glass jars with the floating candle.