many engineers prefer to fit the main panel, keypad and external sounder first

I have always done it that way, and from what other engineers have said "I work Backwards", have mostly believed us panel first installers were the minority.

Its good practice Dave, as you dont get to the end of the day and find you have faulty panel or bell to fit in the dark.

I always fit in this order

1 All cables in and boards, carpets etc back down

2 All protection fitted pirs, contacts etc inc rkp and spk

3 Fit panel and power up ( put in eng mode and leave for now )

4 Fit bellbox and dummy

5 Program and commission system

6 Put all tools away and tidy up

7 Demo system and sort out paperwork

8 Take the ££££ and go home

Job done

Its good practice Dave, as you dont get to the end of the day and find you have faulty panel or bell to fit in the dark.

I would that its not good practice from the way i was taught my craft.

Always to work from the item your feeding back to the supply, this is a safe method of working which makes sense to me.