We plan two ways of doing that. One is that you will be able to tap and hold (you can see that working on Apple apps Health and Stocks, it works really nicely). The second way is that we will “ghost” transactions and events to come, for example, if you have a direct debit coming in a week you’ll see it in the graph (this is not going to happen until we’re a full bank, of course).
If we find that’s a problem we’ll give it a solution. For now we’ll go with a static header, compared with the current app the difference is exactly 1 transaction. Keep in mind that we don’t even use a NavBar on the Home screen so we’re already showing more content and less frame than many other apps,
Not sure if we’ll have it on the first iterations but we’ll eventually let you define custom periods. In fact there’s a hidden detail pointing in that direction in the screenshots of this post. Can you find it? 
Great timing! I think next week it’s going to kick-off the development of that. The second part of your question I think will need to wait until we explore jars/pots and Targets towards savings.
That’s actually how they work, filling from the right. I know it creates a bit of friction but it let us associate the spending numbers with the bar shape a bit better (all it’s aligned to the right). We’ll try it and iterate with users though.