First wave: Assault tripods and scout tripods. Very Limited Veteran Tripods
Second wave: Limited veteran tripods, very limited Dominator tripods. Slaver tripods, regular drones and Grenadier tripods are available. Limited Harvesters and Gatherers. Very Limited Scientists.
Third wave: Veteran, Dominator and scientist tripods will always be limited. Reaper Tripods and drone variants become available. Harvester and Gather tripods are still typically one per scenario. Gatherer Tripods can specialize in Tripod Pilot recovery. Overseers make their first appearance.
Fourth wave: Everything available.
Now: puny human equipment will probably be on a different schedule entirely.
I do like the idea of different time periods, early, mid and late war for example, and restricting the availability of certain units, weapons and equipment to different times in the games background. It Would add interesting flavour and tactical considerations to the game. It's something I've always enjoyed with battletech.
Having different time periods can be helpful in designing scenarios. Human equipment in the early war period is a bit problematic. We have been playing a timeline campaign and have found that limiting humans to infantry, cavalry, an field guns is not a very interesting game. We will introduce Mk I tanks next and see how that goes.
The development of the Humans will be much faster than the development of the Martians, especially at first.
Mark II tanks will quickly become Mark II-B with a 4-inch gun. Chassis will be modified to Mark III also. (I'm considering the impact of running into a "reorganized" platoon of 4 Mark IIIs which will have a 4X4 or 16 gun salute for Marvin. that's 16X.5X.2 or an expected two damaging hits per salvo. )
3-inch field guns were designed to mow down infantry, which they did all too well. Anti-Tripod guns with Ammo Trailers are a game changer.
Perhaps the thing I am most enthusiastic about is the inroduction of the Stovepipe. This weapon gives infantry the ability to aggressively engage Tripods. OOH-RAH!
There was a time period chart available from scot that I've used for every scenario & OOB I've done. I'm repeating it here so you all don't have to dig.
Scotts Timeline for Humans: 1908 Infantry,Command,Machine guns,Cavalry,Field Arty. 1909 Mk I Tank, Heavy Field Gun, *Clamper. *there's some question as to the Clamper as a 1909 or a 1912 entry. 1910 Rough Riders, Anti-Tripod Gun. 1911 Mk II Tank, Assault Infantry. 1912 Mk III Tank, *Clamper, Mk II Mobile Arty., Armored Infantry Carrier. 1913 Minelayer. 1914 Tesla, Mk IV 5" & 7" Tank, Goliath, LIC. 1915 Mk IV Flametank