The real first step is far before an architect RFP. Someone owns some land (or has an option on it), and they decide to look into doing something with it. If they're a developer or a corporation with a facility group, they probably understand zoning, real estate dynamics, and finance well enough to brainstorm and come up with some ideas.
With a developer (one who's survived their first couple projects), one of their core skillsets is to find properties with good prices vs. development potential, and also figure out the sweet spot for a given property -- the highest revenue potential with the least risk at the lowest cost. In a city with restrictive zoning like mine, step one is figuring out how to maximize square footage and saleable/leasable value under the height and floor air ratio (FAR) limits. Detailed understanding of standard and local codes is a big factor, such as setbacks, parking requirements/limits, the various metrics that trigger higher costs due to code, physics, or marketability (for example, go above a certain height and fire code gets more intense, plus the building needs to be stronger, plus tenants like to have more elevator service).
You generally hire the architect before the contractor, but that's less necessary if you have code/concept expertise in-house. Either way, with anything more complicated than a strip mall, you generally want your contractor on board starting in early or mid design, hired based on qualifications, business terms, and general likeability. They'll bring a much better understanding of price, help the architect and engineers think through constructability issues and material options during design, and ask clarification questions in advance. Alternatively, the low-bid method, where the contractor is hired just before construction starts, means the bid price will be a surprise (possibly solved by cutting scope at the end), clarifications will be during construction or as it's starting, and the design might be more expensive than necessary. (I admit bias as a contractor.)
Design takes a loong time. The process depends on how the local jurisdiction approves land use permits (these pertain to zoning or the "right to build", and are very different from building permits, which pertain to specific code compliance). Land Use Permits in my city require major projects to go through design review recommendations, which typically overlap the actual land use application and approval process. Your design will change with design review comments and as the City confirms your interpretation of code. It's best not to design too much until the basic concept is approved, because you don't want to waste that money and effort.
Design stages are typically concept, schematic, design development, construction document, and shop drawing in that order. Each is dramatically more detailed than the one before. Somewhere around schematic the various engineering disciplines are hired, mostly reporting to the architect. Shop drawings are by the contractor and its subcontractors, approved by the archtitect and engineers.
Team formats can vary dramatically. With either option I discussed above, the architect and contractor each report to the owner. Design-build is common (particularly in states with certain tax laws), with the owner hiring a single team, usually with the contractor in charge because they can bond much larger amounts than architects. Integrated Project Delivery (IPD) is a fairly new way of integrating the whole team much more closely and going beyond the typical design phases... avoiding that tangent for now.
One basic point many people forget is that nothing is certain until it happens. If you see a rendering (not a god damn "render", a verb) in the paper for something that will start in a year, even is land use and building permits are easy in your city, the owner has only a vague idea about cost, and neither they nor their lenders are sure about going forward. A lot of people mistake that point about lenders....a lender joining the team is roughly equal to a mortgage firm giving you a letter saying you're probably ok to buy something at a given price...they've done minimal homework so far, and the real decision comes just before the loan is signed. Also, commercial real estate usually depends on multiple loans, including on the equity side, where you or a partner firm provide essentially a down payment.
So many aspects of this. I've only touched the surface...