I've been playing, reading, researching, this period for a long time. The traditional split, based on weaponry, is late 15th to late 17th century. I think that is wrong.
I think the first period starts in the last quarter of the 15th century, and is fundamentally medieval. By that, I mean the nature of the armies, the control exercised on the battlefield, the planning and execution of campaigns, is basically medieval. In the first quarter of the 16th century, the Spanish developed the Colunella, the first example of modern combined arms use, and set the theme for the period through to the end of the third quarter. They of course developed the Tercio from the Colunella, but apart from organizing larger administrative units, there may have been no actual tactical change.
So the first period is a hundred years, and is medieval with some form of capability for combined arms operations. Pikes and shot working in unison, groups of small units of pike, or shot, or pike and shot, moving together on the same command, interpenetrating, exchanging in the same or parallel squares. Cavalry with some capability to be assisted by small shot units (limited to Hugenots), and possibly assisted by mounted shot units.
The second period kicks of in the last quarter of the 16th century, with the Dutch formalising (heresy alert) the ad-hoc Spanish system, and influencing a period of change that lasts to the end of the TYW. This period is typified by formal blocks of pike and shot, varing in size, but basically pike in the middle with a sleeve of shot on each side. The armies have more formal systems of control, with battlefield command structures reflecting what has been established for a campaign, and possibly multiple campaigns.
This period needs to represent the "Dutch System" as it developed, and the off-spring of that system, primarily the Swedish but also the Imperial/Spanish. Units of combined pike and shot work together with other units of combined pike and shot, while there needs to be some flexibility to allow seconded shot to work independently with cavalry, or on their own.
The third period kicks of at the end of the TYW and is effectively the growth of linear warfare. The second and third lines of the Spanish army at Rocroi were German auxilliaries with minimal or no pike. They had been raised from garrisons, and reflected reasonably stable units because they had been in garrison for so long. Apart from the Swedes, most European armies would have formed up in some sort of "Dutch System" formation, but with less depth, and focussed on fire power. The Swedes would add the head long charge to this, and appear to have been quite successful until the rest of the European armies developed a fire system that stopped them. Or there just weren't enough Swedes left to keep it going.
The most common feature of the period, is change. Different types of change, and primarily based on how the armies worked, not what the soldiers did. This is not an easy period to develop rules for, but it will certainly be an interesting challenge.