That's a tall order to fill. It might help if you could be more specific about the dimensions of the workpieces you intend to fabricate as well as a description of the materials you intend to work with (beyond "aluminum") and some ideas about the tolerances that you need to maintain in making your parts. Without information like that, your question is sort of like asking "what kind of car should I get" without providing much in the way of details.
You would do good to get some hands-on experience before contemplating buying any machine(s). My best recommendation would be for you to sign up for an introductory Machine Tool Technology class or two that may be available from a local vocational school or community college, and then come back here and do some reading and discussion.
Some people use 3-in-1 machines because the price looks attractive, however they are generally considered to be an inferior solution compared with individual machines that are designed for specific tasks, due to the inevitable tradeoffs made in the design. Also note that a major problem with a 3-in-1 machine is the need to set up and tear down fixtures when you move from one operation on a part to another. Over time that can become tedious and time-consuming. So I suspect that you will be happier with individual machines.
A lot of hobbyists start with low-end mini mills and mini lathes such as the ones from Harbor Freight or Little Machine Shop, and then they move on to more suitable machines after they have learned a bit. Little Machine Shop also sells starter kits of tooling and other accessories that can give you an idea of what you might need to equip a hobbyist machine shop.
You may find these two guides to be of interest: