Advice please

I think that depends on how often you work out. If you do it every day you should concentrate on different muscle groups alternating them, so when you work out one you rest the other. If you give yourself rest days between work out days you might be better off with a full body program. I also think you should think of this as upper body/lower body because - to stick with the example you gave - most exercises for you back will involve your chest (and your arms) as secondary muscles in the movement.

It depends on what sort of 'workout' you're doing, and it's also down to personal preference. I don't lift, but I do do a lot of cardio, so I like mixing things up and working on a range of muscles, rather than specific groups If you enjoy working on a specific area or prefer a specific exercise which just so happens to work on a particular muscle group, then there's no harm in doing those. If you're exercising for weight loss then any exercise will burn calories, it's not dependent on what you're exercising, just the intensity

As for lifting- the posters above are definitely more qualified to talk about that than I am so I'd definitely take their advice haha.

I just started strong curves, it is full body and the first weeks are bodyweight only and while the moves seem easy enough I woke up this morning feeling like I did 2 hours with the free weights.

Full body HIIT (think super set with up to 1 min between) workouts are best for burning calories. But if that option isn't really available to you. Go with Muscle groups.
My work out plan currently is
Chest/Tri's
Legs/ Shoulders
Back/ Bi's
Core/Cardio(HIIT)
break