Go for the 832, it'll be cheaper to run as it modulates down to a lower firing rate, so it'll be a bit cheaper to run as well as being cheaper to buy
Yep, leaning that way - especially with the risk of wasting lots of money redoing a gas pipe.
Just trying to figure out what controls are needed for adding the cylinder later (and a Wet UFH system). Given the urgency may just go with a Salus one for now and deal with the question later!