Played first 4 scenarios on FM with 2.3 + addon, not to get an optimal core in terms of experience and kills, but to try out different compositions.
Poland (campaign starting core):
1 Pz I A (A2D1 hero)
1 Pz I B
1 Pz II C r11
1 Bf 109 E-1
1 Bf 110 C multirole tac bomber/fighter
1 Ju 87 B Stuka
Norway (only 2 core units deployable):
1 Bf 109 E-3, upgraded from Bf 109 E-1
1 Bf 110 D multirole tac bomber/fighter, upgraded from Bf 110 C (for longer range)
other reserve units untouched
France:
1 Pz III F (A2D1 hero), costly upgraded from Pz I A (not in same upgrade group, only same class)
1 Bison I (Sturmpanzer I) multirole tank/artillery, upgraded from Pz I B
1 Pz II Flamm r11, upgraded from Pz II C r11
1 Bf 109 E-3
1 Bf 110 C multirole tac bomber/fighter, downgraded again from Bf 110 D (for better initiative, especially in fighter mode)
1 Ju 87 B Stuka
Mediterranean:
1 Stug III B (A2D1 hero) multirole tank/artillery, upgraded from Pz III F
1 Bison I (Sturmpanzer I) multirole tank/artillery
1 Pz II G r11, multirole tank/recon, upgraded from Pz II Flamm r11
1 Bf 109 F-2, upgraded from Bf 109 E-3?
1 Bf 110 E multirole tac bomber/fighter, upgraded again from Bf 110 C
1 Ju 88 A multirole strat/tac bomber, costly upgraded from Ju 87 B Stuka (not in same upgrade group, only same class)
Thoughts on those core units:
The experienced Stug III B + Bison I multirole tank/arty combination is quite something. Should have tried that in France already, with one of them in arty mode and the other in direct fire mode.
Will need some more testing, but if I expect a counterattack from the front, I start with the Bison I in arty mode in the back and use the Stug III B in direct fire mode in the front.
Or if I really want to hurt a more heavily armored target and don't expect a counterattack, I start with the Stug III B in arty mode (even with range 1) and then blast the suppressed, armored enemy with the Bison I in direct fire mode. With the 15cm sIG, the Bison I is basically a thinly armored, limping, half-blind SU-152 in 1940. But a direct hit from a 15 cm shell is still devastating for armored targets and tanks even in the later stages of the war...
Third option would be both in arty mode, either to cover each other or to cover more friendly units.
The Pz II G is pretty versatile, due to being a pretty fast, tracked unit with recon movement, even though it only has a vision range of 2.
On the other hand the Flammpanzer II is quite something as well, making short work of entrenched infantry. Especially when supported by arty. The combination Stug III B, Bison I and Flammpanzer II might be well worth a try sometime in the future.
Anyway, imho a lot more interesting variety of viable options, compared to different ratios of the latest Panzer IIIs and Panzer IVs.
The multirole aspect of the Bf 110 is pretty useful and makes this often overlooked backbone of the early Luftwaffe really good. First the supporting fighter duty against the enemy airforce, then the ground support later on. The changing role of these aircraft imho also adds to the immersion. Plans and planned uses of equipment have to adjust to the situation.
The Ju 88 A multirole has some nice suppression options, but I still prefer the Ju 87 B to rack up the kill count in the early campaign. Just for the hero alone, but also because Barbarossa provides a lot of strat bombers, don't really need another one.
Thoughts on Barbarossa:
Any prestige spent before the last turn of the Mediterranean scenario would use old, "tactical" prestige, before it is wiped due to your promotion and prestige becomes a strategic resource.
So costly upgrades (eg from Pz I to Pz IV chassis) should be done before the Mediterranean scenario ends, even if that costs some minimal experience or kills.
If I would continue with this core into Barbarossa, I would probably try to adjust a few things:
Costly upgrade the Ju 88 A back to a Ju 87 B before Mediterranean scenario ends due to the prestige reasons stated above.
Then at the start of Barbarossa upgrade the Ju 87 B to a Ju 87 R for the longer range.
The Bf 110 E can stay, while the Bf 109 F-2 is upgraded to a Bf 109 F-4.
Not so sure about the ground units. Maybe the Stug III B + Bison I + Flammpanzer II is worth a shot. On the other hand, there are already Panzer Is and Panzer IIs in Barbarossa, waiting for cheap upgrades. So after the experiments in the early campaign, one or two Panzer IVs are probably more helpful, given the existing units of Barbarossa. And the expensive upgrades from Bison I and Flammpanzer II don't even cost "strategic" prestige when they are already done before the Mediterranean scenario ends.
For the next addon update, I have to find a way to make that "upgrade before Mediterranean scenario ends" less annoying.
And also have another look at the primary mode of the multirole ground units. Even though there is imho little reason to change back from a Stug III B to a Panzer III H.