A few thoughts for you:
As you have a limited wardrobe, I would speak in terms of maximizing combinations and use. For this, a solid navy jacket is supposed to be the most versatile piece of men's wear and would go with almost any color scheme, except most navy/blue pants. Solid greys are highly recommended as they can partner with most anything and are quite versatile. I would suggest a light and dark pair of grey pants after the navy jacket as they will tend to go with a wider range of shoes/shirts/jackets. For shirts, simple colors are more formal with white being the standard and then moving to light blue. You will want a couple shirts in this color range to start for a more classic look, potentially with light patterns, then you can move to more powerful pattern/color combinations. When pairing items together of similar color scheme, you need to make sure there is enough contrast, otherwise you will look like you did a poor job of trying to match the same colors. I am slim, so I won't comment on if patterns are slimming or not ;-)
There are lots of guides as to which shoe colors go well with which pant/suit combinations. I posted a link I like below. The biggest thing here is that you want complementary colors with appropriate contrast. For example, I would typically pair darker brown shoes with darker grey or blue pants and lighter colors together, but this is a general rule and any combination should really be seen together as you are figuring out your color combinations. I have seen many "exceptions" to rules that look quite stylish, depending on how loud you want your outfit to be. I'd say to start toned down and stick with the classics first- figure out your basic style and then move on to more accented pieces. Outside of that, keep in mind that less decorations (broguing, wings, two tone, etc) and darker colors tend to mean more formal wear. Starting out, you will want a basic oxford and blucher (brown being the most versatile & burgundy also pairs quite nicely with a range of clothes), which can pair with most anything, then you can move to loafers and other more style/casual pieces. As others stated above, this really depends on where you are, tech in the bay area or office work in Miami would be much more accepting of casual looks than work on the northeast cost of the US or London.
A couple things to not do:
As an American who has moved to Europe and upgraded my fashion the last few years, I cringe at the fit of my old clothes. Make sure the shirts are tailored to fit your frame, pants as well. I can't emphasize enough how much extra bagginess is a turn off for men's pants. Lastly, stay away from box toed shoes altogether and you will do just fine ;-)
I hope this helps- feel free to share more information about location/industry/etc and we can give you more specific advice. Also happy to recommend brands if you can talk about price range/quality that you want.