Buy one each of the 135mm, 275mm & 450mm you will be pleased having all those lengths for different engines.
Get one of these for the disposable camping gas bottled (brilliant) -
https://www.forest-classics.co.uk/ceramic-burners/gas-essentials-and-jets/gas-valve-for-disposable-tank
One of these for refilling with the super cheap camping gas -
https://www.forest-classics.co.uk/ceramic-burners/refillable-gas-tanks/refillable-gas-tank-small
And you will appreciate one of these greatly -
https://www.forest-classics.co.uk/ceramic-burners/gas-essentials-and-jets/bix019l-long-spout-gas-refill-adapter
Depending on what engines or separate boilers (like Stuart boilers) you likely to own in your steam addiction (trust me it doesn't get any easier) a selection of these
and one round one will also be very beneficial. The BIX gear is just terrific kit to have -
https://www.forest-classics.co.uk/ceramic-burners/rectangular-burners