My 5 year old would probably help himself to treat food as well OP, so don't panic. My 3 year old seems to have a lot more self control with snacks, I haven't done anything differently so I think it's just their way. I wouldn't beat yourself up over that aspect.
I've got everything like that in a high cupboard and they can have it in moderation, then they're is a drawer they can reach with healthier snacks - rice cakes, crackers, raisins etc. Stuff they like but won't eat for the sake of it. Maybe I am demonising some foods and of course it would be great if they were both like the 3 year old, but they're not and what's the alternative - let the 5 year old eat as much junk as he likes and have weight problems before he reaches secondary school? Hopefully self control is something we can work on as he gets older, but allowing him to become overweight now isn't going to do any good.
I reckon you probably do have to get up early with her though. Mine is an early riser, although he will usually come and get me/I hear him and wake up before going downstairs. If he did go downstairs the TV remote would be out of reach anyway because that's where we happen to keep it, so he's quickly get bored. I don't really have an issue with the TV in the mornings though, it's more that something else could happen whilst she's unattended. Is he noise of her going downstairs not waking you up? Or are you just trying to go back to sleep because it's so early? I think she needs to be told to come in and get you/her Dad and you need to go down with her, let her have the telly if that makes it easier while you wake up slowly with a coffee or whatever. I have actually come to quite like the early mornings. I stick the telly on and if I've got lots to do I crack on with jobs while he's quiet (washing, prep tea etc) or just chill out for a bit before the day starts.
I wouldn't beat yourself up about keeping the food out of reach though. I know the modern way of thinking is to not have any foods off limits so that children learn that all foods are fine as long as you moderate them, and that's great if you have the sort of child it works for, but they're all different.