By the way, is there any type of factory (eg advanced) which can communicate and send (excess) resources to others of its type, ala the research centers? Or maybe this is already achievable with logical circuits? Also, can you use such to make factories not stop production when they reach the rather low default product number, and carry on for longer without having to feed anything?
It's been a while since I tried it, but I think you might be able to use inserters to grab inputs from one factory and move them to another? Although if I have multiple factories needing, say, iron plates, I usually just try to have the belts run by both of them.
The limit to the output pile is a hard one. I see you already have some iron chests storing red beakers; those are the way to store large stockpiles. Notably, you can set how much they store by clicking on the red 'x' at the end of their inventory, and then blocking off part of their storage. Very useful if you want a buffer, but not 1600 items in the buffer.
Mid-late game, there are logistic networks supplied by flying robots. Which can certainly easy getting parts to various types of factories.
Also, your base looks fairly well-constructed. You should have seem the spaghetti base I built not too long ago.
I suppose there is a way to set up those storage boxes and tied pickers so as to look for the number of available x on the belt and accordingly store or leave it alone. Have to look at a video for how to do this.
Alternatively, is there any upgrade to the long-arm moving mechanism? So as to go with the cheap double-belt approach (although I'd rather not).
I don't think there's a way to evaluate how many are on the belts. If you use the red 'x' limiter technique, and there's no more space, the inserters will leave anything on the belt alone. You can also use the red and green wire to connect to storage boxes and inserters and set various conditions based on the number of items available. Combined with logical circuits you can make things quite complex, but I tend to stick to simple thresholds, if copper < 500, enable the inserters that load more copper ore, otherwise don't. That sort of thing.
Wires count up the sum of everything that color of wire is connected to on that network, so it can be also be used to count up the sum of goods in a bunch of boxes. If the sum of all the coal in my power storage reserve boxes is less than 20,000, send more coal from the mining area. Otherwise, let that coal go somewhere else or stop mining it for a while.
Inserters always place items on the far (IIRC) side of the belt, and a belt coming in from one side puts its goods on the near side of the belt. With this in mind, every belt has two sides that can carry separate goods. I usually try to avoid having multiple types of goods on one side of a belt because it tends to get imbalanced over time and then one or the other of your factories can't get what it needs because the other type of good is blocking its inputs from arriving. Alternately, filter inserters (the purple ones) can be used to weed out particularly types of items on a more-than-one-item-per-side belt and put them in storage or on another belt to somewhere they can be used.
A note on unintended side effects of logical conditions on the factory:
Once Factorio night I was running around my partially-solar-powered factory making some upgrades, and all of a sudden the lights started turning on and off at 60 Hz. I thought there was a bug at first. Nope, not in Factorio, just in my factory. I still had some coal plants running too; with lights and radar, and my recent additions to the factory, the batteries were draining at night. But with lights and radar off, the batteries were being recharged by the coal plants at night. So every Factorio time unit, the lights were alternative between on and off, creating an impressive strobe effect.
The next Factorio day, I upgraded my logic to turn the lights off at a lower threshold than the one that turned them back on.
Poisonous wolves, wolves with Force powers, wolves that perform scenes from musicals... eh, whatevs.
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), but the removal of finding the occasional gun and ammo takes too much away for me.
Let's do it together!
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Take my [goshdarn] money, you pieces of [filth]. It's just an announcement trailer - isn't even a release date yet; might be trying to time it with the release of the Mahershala Ali movie - but it tells us that the game takes place in Paris during some kind of epidemic that has people sheltering-in-place when the Sun goes down. Well, most people. Some mother[lovers] always tryin' to iceskate uphill. 
