Limestone resource needed

That is a major component in concrete production. For simplification, sand and limestone ores should go into "concrete mixer", not just sand like now - it is oversimplified, IMO.

More realistically (yet, not ideally), the limestone and sand should go through furnace resulting in cement product (u-shape conveyor output) first, before entering the concrete mixer.
Taken that the Blast furnace has only 2 inputs (so one must be coal), my suggestion is to add "Cement" recipe for Blast furnace where it is produced straight from limestone "ore", with output product coming from single u-shape conveyor output without use of molten channels. And then cement plus sand and water can go through Concrete mixer resulting same product as before.

Whilst I agreed, did discuss this with Filip the other week, and apparently they did originally have limestone as an additional resource, but found it made the early game overwhelming having to set up more mining areas.
Personally, I'd like to see it added as an ingredient to cement mixer, with a later recipe to premix sand and slag.
And as an additional component for blast furnace as metal ores are mixed with limestone before entering blast furnace to remove impurities.
Does make things a lot more complicated though ...

I perfectly see that early game is overwhelming, but IMO the issue is not so much a complication of production chains, but rather a result of attention-spreading issues here and there. Problems start to rise too early making player scared to explore, try and experiment. My suggestions to fix it:
1) Make deconstructions result in 100% materials returning.
2) Reduce maintenance demand.
3) Increase buildings productivity, especially furnaces, casters and assembly plants (or lower buildings cost).