They way I think you can calculate the optimal expo count from an econic perspective.

In a normal sn start one ussually explorres 38 expos. Exploring 58 means an additional 40k investment.

At 58 planets your start built could include 1700 CF. To earn your first 40k you will need to let your cf built (5 ticks) and generate 2 ticks of income. Exploring 58 as such lets your econ lag behind 7 ticks on a 38 planet start.

With a 38 expo start you can hit 100% ob and 100k income at day 3. At that time you will need around 8 ticks of saving to get out the additional 20 expos. At this point both starts perform around equally.

One reason for 38 start could be that at end of day 3 you want to sent out more than 20 expos, which is relatively cheaper to explore than with 58 start.
Less nw which helps players that heavily rely on science.

Main reasons for going 58 from the start would be, more space to prevent early ob-cost, more claimed space early on securing systems. More pop income.

Pie still needs to confirm if there is a delay on attacks. Based on accouncement there is only a delay on ops.
" Offensive Operations Delay: 1 week (unchanged)"

Regarding optimal expo count. With 50X resources and 1 week attattack delay i think even at 75 expos i would still max expo.

We had this discussion on discord - he said to his knowledge that the week also means for standard attacking

I'm exploring 10...I don't know how to math past that.

I haven't calculated anything but really the only question is the attack delay. As long as all planets can be defended by the time that delay comes around it's definitely the right decision to take the massive savings from sending all explores with a pcount of 1. The no cores makes it slightly not comparable to the 38 planet start since you didn't have to portal half of those or so.

It looks like it actually does NOT include attacks.  I don't know if I like that, but that's how it works at least for this next round.

So it literally is just spells/ops that won't work.