What are you using to make cuts?? Maybe show us your setup and we can tweak it for you.
That there is above a beginners level but you are right when it comes to drilling for the tube.Just to add to what JT has said..
You will also need ensure you can drill bang on in the middle.
I actually prefer to do scallops on round stock and indexed in my lathe. Then a jig to guide a router to cut the angles. The beauty of this method is every cut and even the hole is done about the centre point only.