Hi MayLittle,
You must be rather confusing now but its ok =) let me answer all ur enquiries.
2 way cake itself is a foundation.. which is why its also call 2 way foundation. Between this and liquid foundation, liquid it comes in a variety of texture from sheer to heavy or full coverage. whereas 2 way cake has more denser pigments therefore gives most amount of coverage.
When applying liquid foundation, it will be better to complete with a loose/finishing powder to give a more smooth, even and matte finish. otherwise, some liquid foundation may feel abit shiny and sticky on ur face.
For 2 way cake it will be no problem applying on its own as it comes in a denser powder form and will give u a smooth and matte finish upon application. Some people like it for its convinence.
A loose powder is something like a finishing powder that can also be found in a compressed form which we call press powder compact but the coverage wise will be lighter compare to 2 way cake. In fact, among all powder and foundation, it provides the lightest coverage. Therefore, there are people who really like/prefer light makeup they just apply sunblock and a layer of loose powder. But unless u have really perfect and flawless porcelain skin, otherwise, i'll recommend that u use as a finishing powder after ur liquid foundation.
There are many type of makeup base nowadays in the market. Most of the texture are usually light and sheer and mostly comes with SPF protection and some even provide skincare properties. It is not a neccessity but it somehow does helps in providing a better finish and helps makeup stay better and longer. Just like an artist painting something, he needs to set a base for his canvas so he can draw better and the painting stands out more.. the theory is about the same here. =)
Nowadays there are many different type of foundation and powder in the market. So its very important that u chose the right one for ur skin and feel comfortable wearing it. Like i always told my makeover clients beside choosing one that its suitable for ur skin type, chosing the right shade is also important as i do encounter ppl telling me that they always chose the most lightest shade of foundation thinking that it will make them look fair and white which is not the right way. When buying a foundation always feel free to try out..best will be try on the face along the jawline or on the chin area, that way u wun go wrong and will most likely to get the right shade. =)
Hope the above will be helpful to u. =)