Edit: Some calculations where wrong, corrected.
Thats exactly the problems you get confronted:
1. solar vs. stying at coal.
Pro staying at coal only:
This is not so easy to answer. depends. For example: I tried this time not to use solar and came now to a point, where I got 20 steam engines (about 10 kW), I could need a bit more, but it handles that (about 50 mines, about 30 factories, no lasers). This doesn't need that much coal, about 1-2 coal per second or so. My coal field is only 3/4 empty after 12 hours, I don't use lasers, only guns. So AFAIK no problem.
When going to solar you need time to place all the stuff. I found out a layout with one energy station in the center placed in long lines is most efficient to place, but even with that it takes some time to produce the panels and some to place it and in this time, I surely extended my cheap and easy to install engines for another line with 8 engines. And you are not finished with that - you will need about the same amount of accumulators and still need backup power for the case, that everything goes wrong. And backup can only be done with steam-engines. So, you need steam engines, no matter what and the question is just: How much coal should they use. And don't forget about the amount of resources to built a solar panel and a an accumulator.
Pro switching to solar:
With solar energy you can completly forget about coal. No need any more. This spares diging for one resource, which is 1/3. It's easy to build it so big in one flow, that you never need more. You can switch off the steam engines with some simple tricks and then you don't need to think about energy problems any more. Simple. If you make it big enough, you can make it big enough to be sure that you don't need any steam engines. The devs said, the want to have the creepers going against air-pollution. Clean, green energy is made like that!
[currently I think a compromise between steam and solar is a very, very fine idea! There are 2 reasons: You will not Steam-power for everything which needs a constant flow of energy. Depends on your priorities. But for example: Smelting during the day looks for me like a very clever idea and I'll try that out! The problem, which I see here is, that it is difficult to keep the different electric networks separated. I also would say, that using a radar or the research, cries for soloar enegry and accumulators, because they need very constant power and you don't need to regulate this very much (just enough panels to get the accumulators loaded and just enough accumulators to come over the night).]
2. Trains vs Belts
Pro belt
Usable in an area of about up to 500 tiles. (500 is very, very far! to compare: radar is 100 tiles). More is of course possible, but it takes 4-5 minutes, till the first resources are transported to you then! Use the car for that! Belt is much cheaper, the basic belt is unbeatable. even if you use 2 in parallel, which have the best price performance ratio. And think to the complicated train-stations and signals you need to built when you want to have some performance. It takes an hour to built all that, so that it is working well. And you need so many inserters, chests, and other stuff and trains are volunerable, so you need to protect them in the station, which will cost extra time to built.
Pro train
Trains make sense from about 200 tiles upward. Every wagon can transport 960 items of ore. A basic belt can transport only about 700 per minute. This means, that if you manage to bring one train per minute to your main-station and it has 1 wagon you have a bit more transported, than the belt in the same time. Of course you can built faster belts, or more belts in parallel, but the cost will then be equal or higher to the train-track. And this is only for one wagon. 4 wagons are good to handle and with that, the throughput is 4 times more with the track, just by adding some wagons. The same is with more trains. And not to forget: trains are so much faster than belts, 500 tiles is just half a minute or so... so you see the stuff earlier. And the last reason is: Per tile about 6 items are "stored" on a belt, so with 500 tiles of length you have a storage of 3000 items - half a chest! This is much and you can't use it in this moment and it takes minutes, until you can use it. The train doesn't need so much storage, or in other words, the "blind-capacity" is much lower. (BTW: It can be really handled like the electrical capacity of a wire!)
....
I currently think, that even the default sandbox-game has so much resources nearby this 200-500 tiles around the starting-point area, that trains are not needed. Otherwise it is difficult and take much, much longer! But still possible. On low resources, you need very much time to fetch all resources and don't have a chance to go without train.
What's here needed is the certainty, that there are some big resources anywhere around you and about the direction you need to search them. A resource-radar? Or some other device which helps you to expand the map for resources in an diameter of 1000 tiles or more.
Only in this mode the train is needed then. I currently think, that after exploring the surroundings it makes sense to built a train-track into that area, where are much resource. Everything in that area is transported via belts to this outpost-station and from there transported to your base. Once you created that line, it's easy to extend it and
I think trains for such a long distance make really fun! (I recommend really to build such a long track, you will hate it, but when it is ready, everything works as planned and you ride on it it it's really nice!)
Some things are also needed: Some "Blue prints" for stations (or a special buildings), because the micro-management of building and placing all that stuff (and not to forget to transport that from your base to the outpost) is really, really hard and I think this isn't much fun either. Also some help to built tracks (I hate to built 45 degrees tracks!), building and placing the wagons, the programming of them, the signals etc.
PS: The productivity modules are really great. I haven't much experienced that yet, but it looks like they change the balancing completely; what's before that was bad is now good and vice versa.
I currently think it is hard to change the factory layout so that you change from a "belt-based production" to a "logistic-bots-production", because you need so much stuff to research for that and then you don't know where to put all the old stuff in (I really want something like a recycler). But this is part of the game.
But the next factory I would built differently from beginning, to avoid the problems with changing the production-layout.