i think 3 days a week is good. You have a hard job, so consider that in when you train as you are using more physical energy in the job then a office worker, So recovery would be your best friend.
Always condition your body when you start, 1-2 exercises for large muscles, chest , back, legs, shoulders. 1 exercise for calves, forearms , biceps , abs.
2-3 sets, total body workouts... progress VERY slowly by adding in 1 extra set or few more reps as the weeks go by, dont be in a rush to perform a routine from the internet, we are not all made the same. Don't train 5 days.. just go slowly , enjoy it ... have fun, this is your time for yourself. DO NOT train too heavy or too failure.... strong enuff to do 10-12 reps , but do not over do it until your body is conditioned.
I hope this advice helps.