Howdy! I've out about 5 hours into the mod so far and am generally really enjoying playing through and figuring out how things work.
In particular, I really like how you're heavily encouraged by the small starting resource patches to implement loops where you deconstruct items to multiply your base resources.

Everything through the early game went pretty smoothly, but as soon as I started blue science, I felt my progress really grind to a halt. The amount of fish required per science pack seems like it really exploded at blue science and I would say doesn't really match the resource requirements of everything else.
I'm curious to hear what you would expect players to aim for in terms of science/min in this modpack.

In Vanilla, I think 45 science/min is a fairly standard target for players (that's 5 red labs, 6 green, 12 blue, a fairly standard ratio). In order to achieve that here, with each blue science pack requiring 338 fish, it would take 7.6k fish/min. That's 4.2 full red belts! At this point it's starting to become an issue of just routing enough belts. Looking ahead, I can see that it's going to be even crazier at purple and yellow science (yellow science is 12.7 full blue belts of fish at 45 science/min). It just feels a bit ridiculous considering a nuclear reactor is only 506 fish.

So I would personally recommend that you scale down the amount of fish required per science. I think it could be an interesting logistical challenge in a vacuum, but right now I think it's just causing research to crawl along. I think that encourages AFK for research, which I believe is not a very fun gameplay loop.

Also, separate question: Is the mod meant to randomize the recipes in each play through? They are the same for me every time (which I don't think is necessarily a bad thing; it could allow for better balancing).

I agree that the science fish costs are at least a little too high, I set them high because the ability to multiply resources necessitates a big resource sink somewhere, and research is the obvious place to do that. I'm thinking over some alternatives right now but in the mean time I've reduced the fish multiplier on science to something more reasonable. (I had actually set the science prices, and then later on fixed a bug that caused them to go 2-3x higher)

As for the randomization: there's an option to set the seed on the mod settings page.

Ah, that makes sense. I do agree that with the somewhat exponential growth of your resources, a bigger sink somewhere is necessary, and I do think that research is the right place to do it. Perhaps you could look into spreading that cost out more across the different ingredients in the research? So less fish, but more of the secondary ingredients. That way the total throughput needed for each ingredient is a bit more balanced. I've noticed that for a given science, I need a lot of assemblers for the science itself, but quite a few less for the ingredients. For example, on the base seed for blue science at 45 science/min, I'm using 12 blue science assemblers, but I only need a single sulfur chemical plant, a single assembler making trains (and then deconstructing them into engines) and a single modular armor assembler which deconstructs into red circuits.

So if you increased the other ingredient requirements while decreasing fish costs, I think it might balance out a little better. It would also further encourage using more advanced recipes and then deconstructing them over the base recipes, which I think is a good thing.

Once again though, great work so far!