Since the format is fresh and hasn't even really started elsewhere (I think Oct. 5th is the official release) we have no "legit" pro decklists out yet. These are the closest ones we have so far. As you can see when the format is fresh, more aggro-ish lists do really well as slower decks aren't yet too much tuned to beat them.

How big of an investment you need to make to get started? It depends on entirely which of the 2 color decks you get from dailies (they have 1 good land each and some have very good rare/mythic while others have trash). Some of the starters are already plenty playable and upgradeable but for real deck I'd say you need few good cards from your initial pool, the 5$ welcome package and around 50$ spent in gems. At least this was my experience setting up my first 2 color deck, yet I still missed some rare lands as they are often the bottleneck and it gets worse if you want to play 3 colors.

Whatever you end up doing, settling on a deck and focusing all your resources towards it instead of spreading them out will let you achieve a playable version a lot faster. If you have a list in mind, open the packs you still miss most cards from.

Obviously any extra cash spent will ease it up, F2P is most likely possible but if you don't get some of the better 2 color decks you will have to spend a lot of time to progress.