Let’s be very clear, it’s almost impossible to reach core team perfection at the Seed and Series A stage, but you wouldn’t be reading this unless you liked almost-impossible goals…
The core team in perfect alignment is a thing of beauty. Three well balanced individuals who support each other creating a gapless barrier to take on any problem. Well…. it won’t happen. But that’s ok. This isn’t about a perfect team but rather the goal of striving for one.
Critical is not the actual individuals but rather the traits which they possess (which in some cases can be learned – so don’t give up hope yet!) Vision, Sales, Product. Let’s break these down.

Vision: Very common and most appropriate is having the visionary leading the company in the Founder/CEO role. She inspires colleagues, VCs, customers, and future employees. Selling the dream is a vital element as it touches so many parts of the business both internally and externally.
Sales: If one person sets the work ethic bar, it’s him. While the Visionary often focuses on the sales front as well, this early stage team member is the real sales muscle. Later he’ll often move into an operational or 100% sales role, but for the time being, this jack of all trades leads-by-example with sales, then follows up internally pushing the business forward.
Product: As you cleverly might have guessed, this person has one clear focus, to make the best product possible. While finding an amazing product focused core member is difficult (an expert in programming, architecture, systems engineering, user-interface, etc.) you know that you have hit Product-Leader-Zen when they say, “it’s not perfect, but we can ship it”. “Ahhhhhh” (exhaling with a smile). Engineers like to overdevelop and perfect anything they build, which is correct, that’s why they often became engineers, but the Minimum-Viable-Product or 80% finished model is what actually gets shipped (the reality is that it’s often only 50% finished). This is how you get to market first, beat you competitors, get through that feedback loop faster, and end up gaining market share. Find a head of product who understands this and hire them!
Do you have an advantage the faster you get these three types of individuals on board? Yes. Will you create this perfect team? Probably not. Does striving to achieve the traits of these three core team members help your business by creating alignment and clear definition of your roles help? Absolutely yes. Worst case scenario, you know exactly who or what is missing, which is a really good starting point.
If you do achieve core team perfection at an early stage, please let me know, and the first round is on me!