Scout (19 weeks on Friday) is fed on demand, basically ebf (with the odd bottle of formula thrown in, because I know I want to mix feed from about 6 months when I have my exams, and didn't want to risk her having a benny about it! also because I wanted to see if formula would make her sleep through anyway, digression.)
she has no routine really - she can go 4 /5 hours, but equally sometimes wants a shorter, snacky feed after only a couple of hours or less (am hazarding that this is more for thirst than hunger). I don't even bother keeping At night she wakes every 3 - 4 hours like clockwork to feed and has done for weeks if not months. I'm fairly happy to go with the flow - I don't see how I could get her to go for longer stretches / overnights because once she's decided she wants the nip, she will shout and shout until she gets it! and I don't fancy that at 4am.
re tummy time, do you use a little half moon pillow (we got one with her playmat) or rolled up towel? that really helped build up time with Scout, it stopped her from eating shit on the rug in the early days which she understandably found rather discouraging