olivia_tinker

I don't think it's really possible nowadays, depending on what and how much do you want to add. Old games arten't any comparison of sorts - they didn't weight much mostly because they operated in ultra low resolutions and very limited color pallettes, had no voice overs and music was limited to a couple midi/fm/mod tunes at most. As much as those games could easily fit onto a couple old floppy disks, modern games work on much higher parameters and as such, their requirements grew exponentially. Obviously, you will want that, because it's considered a standard for nowadays software (32bit graphics with at least 720p resolution output + full mouse and keyboard support), that allows decent enough experience and ease of use.
It is still possible to create lightweight games, albeit that would require some knowledge on how to optimally reduce the filesizes of your games assets and/or utilize techniques, that allow massive reduction of space and little to no cost in terms of quality degradation. You might be interested to check out Ren'Py. As much as it probably won't be possible to fit a game under 5 megabytes (due to it's shared libraries, that are required to run games), you can still make games, that won't weight more than 25-50 megabytes at most (depending on how much content you'd like to fit). Creating retro-esque games are one such possibility. such games (or software in general) mimic the old hardware limitations from an aesthetic/visual standpoint, which in end makes them much more lightweight and less demanding in terms of required computing power (as such, they can potentially work on much older/slower computers without any discernible performance loss).
Anything below would probably require you to switch to either one of self-sufficient web-based engines (as Palas mentioned above), or resign from advanced sound environment and modern, high-res graphics. In other words - a text based game.

Last week I saw a homeless guy with a smartphone here in Warsaw. Access to information and possibility to leech on free wi-fi around the town are sometimes too attractive to skip even for those that theoretically have nothing. :>

Well, I never heard of somebody actually doing it.  Well, technically it is possible, I think, if the VN is simple enough, but there are way too many problems with it. The main problem is that I really doubt that such VNs would sell. If you market them for a developing country where people still can't afford smartphones (I assume that the VN will be in the language generally spoken in that country), I really doubt that the same people would have enough money to spend on entertainment, and such ports would never sell well enough for the trouble to be worth it. Also, mobile phones have a lot of different OS's, while most smartphones use either android or ios, so porting that VN to different phone models would most likely be a nightmare.
Also, the information in this article seems a bit old. Here in Russia, for example, the market right now is dominated by affordable Chinese smartphones. I think, the most people who still use basic phones are elderly people who aren't very good with technology and aren't used to touch screens. And, I guess, the poorest people who can't really afford anything. And a small percentage of people who are too afraid of spyware.

In most cases no, unless you program the game exlusively for such devices or put a lot of effort into creating a heavily streamlined version of your game dedicated to them - usually those phones have brand-specific operating systems and very limited processing power, so they won't be able to run normal PC or Android apps. I also can't imagine reading VN text on those tiny screens would be a pleasant experience.

I think the list pretty much covers all the parts needed to make a VN. However it miss out on one important issue: planning.
If you write a VN, you need to plan a storyline, design character personalities etc, just like when writing a book or a movie. I wrote more about how to do this already in another thread, where I also writes about script design from a programming point of view. It's more like a howto guide and a proposal for one approach to solve the issue, but it should give an idea of the kind of work, which this step requires.
 

Before people smarter than me can elaborate, I think I can pinpoint basic elements. To make a VN you typically need:
1. A game engine (most likely Ren'Py, which is free and have a lot of guides and assets available for it)
2. A graphical user interface (GUI), through which people will interact with your game - Ren'Py provides a basic structure for your GUI, but custom visuals and ability to modify the UI according to your needs is important.
3. Background graphics - static images over which character sprites and the GUI will appear. I think it's easy to find free or cheap stock VN backgrounds.
4. Character sprites - the representations of the characters involved in your story - static 2D images, usually with a few poses and face expressions to fit different situations.
5. CGs - custom, full-screen illustrations which show situations that are hard to present through sprites and text, usually used in crucial moments of the story.
6. Background music - to give your game a proper climate and make it less monotonous, underlining the switches in mood etc.
7. A script - all the dialogues and descriptions that will show in the text box (which is a part of the GUI), along with necessary "stage directions" [especially if you'll not be the one handling the programming, the person doing it must know what background, expressions etc. go with each scene].
8. (optional) Voice Acting/Voiced Narration - expensive as f***, if you want good quality, so many developers skip on it.
9. (Optional) Other sound assets - depending on the content of your story, some additional sounds could be useful, for example if you want bring the reader's attention to something, but often such additions are quite obnoxious - music can be enough.
When you have a script and all the necessary assets, you have to put them together and synchronise them properly. This part I know pretty much nothing about, as I'm not a programmer.
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20 edits later - Did I miss anything?