I think you should include all that you can. If it only helps one GM then surely its worth it. GMs who don't want to use all of it don't have to. There is a contents page for them to skip to the stuff they want.
As much as I would like to do that - I can't. The book will have a print edition and a download so I need to limit pages. I also don't like including too much as games that are too big cease to be manageable.
1. examples of the rules in use 2. Cheat sheets 3. Example adventure 4. Secrets bits of the background 5. Plot hooks 6. A series of tools for running Icar Sandbox campaigns 7. Some home truths about the system
I think the stuff like 5,6 and 7 could be left out and published on the icar website if absloutly nessisery. After you've released v4 and you're happy with it you could always write adventures for it, which would include 5,6,7
I hate secret background. My players have invariably already read it, or will read it once they start playing but before I can bring it up in play. Maybe a section highlighting mysteries and possible secrets that explain these mysteries, a couple choices so the players will still be at least a little surprised. "He chose that one?!"
Plot hooks aren't really necessary if the players guide includes campaign ideas.
Sandbox Tools? Is that stuff like random system generation and random alien encounters and stuff like that? That's always a lot of fun. That can go on a separate GM screen.
Home truths about the system might not apply outside of your home.
That would actually make the GM Guide more of a Campaign Guide that includes GM cheat sheets.
The GM's handbook for CyberPunk-2020 was called "Listen Up You Primitive Screwheads" and carried a notably antagonistic tone. This was in large part because the poor GM of that game had to deal with characters that often had cybernetics, combat drugs, corrupt corporate connections, heavy fire power and underworld backing. While I wouldn't frame the ICAR guide in such a way, similar issues of players with amazing abilities will probably crop up, and means to counter them should be touched upon.
What do you do with players/characters while one or two in their midst are off in the net or operating the star ship? Once again looking at Cyberpunk, there was the infamous "Decker Problem" where only the Netrunner could use the advanced net and hack with his brain, going on an adventure entirely of his own while everyone else watched. (Not helped by the fact this should be only seconds of game time, so they can't be off doing other work.)
Making of commentary, or discussions of your game might be nice, but its hard to judge an audience's tolerance for such prattle. Maybe a page at the opening of each chapter addressing why Gaia is hard light, or how you came up with the ideas for each weapon but a running commentary or a number of sidebars might be too much for some people.
Secrets are good for the GM, and maybe an outline of how to run an adventure or tables of what they might encounter. However a full adventure in itself doesn't seem like the best use of space. If it gets run at all, its really only useful once, as opposed to including more advice about how to get the game moving that will always be helpful. Cheat sheets should probably be in every book, rather than just the GM book. Pre-made characters that can be NPCs/replacements/given to new players to short-cut creation might be nice though there is a fine line between just throwing stat blocks at people and and providing something useful.
One thing I always wanted to do in a game that had a GM's guide (notably XenoExodous) is to make the GM supplement a special edition sort of book. The main book has small monochrome images, mostly of the occasional item, place, or person, but is kept cheep for mass consumption. Optional books get full color plates and large illustrations to reward those who buy them, and make the book something to show to the players, rather than one person's esoteric volume. One really fancy idea would be to add extra flaps and clips to the inside covers, so that it can be stood on end as a GM's screen - but that might be a bit far fetched.
@Misterecho Cheers Gordon, I'll create the stuff in that order, so make sure it goes in.
@Sheikh GM Screen. I've never used one so I am not sure what a good one looks like. Also, as Icar is a free download, I might have to do that as pages you print and stick together perhaps?
I like the idea of having multiple secrets to explain a single facet. Sort of like plot hook examples but for setting background.
Sandboxing isn't random roleplaying. Sandboxing is a method of setting up a campaign which is not linear and has many story lines running concurrently. The characters are present at events and then can either take action or just ignore that plot.
Home truths are things like "Icar is DEADLY" and "You need armour or a medic or both if you have a gunfight". New GMs are likely to fill their campaigns with guns and then realise people get shredded VERY easily.
There will be a sample setting and campaign as part of the book, so that will be split into two aswell.
@CA - I'll break up some answers...
Splitting up the group In space combat, the new system is all inclusive of all the characters, so no-one should be left out. At the very least, a character can be trained relatively easily to be useful on ship. Although Hacking (Netrunning) is relatively divisive, it isn't as deep as CP2020, so should only require a view dice rolls - like any other skill use.
Making of... Belongs on a website and is fluff.
All the other stuff I like. As Icar in Core form is broad, NPCs will be very Setting specific so will go in the Setting bit.
I like your other book ideas but I am going to produce just one Icar book at first. Everything you need to play in one book - core rules, setting and GM guide, cheat sheets, the lot.
Useful things to me would be things like random spaceport generators, archetypical NPC mooks, and the like. A good section to add would be How to Run Icar the Rob Lang[tm] Way. Using myself as an example, I do character voices and mannerisms, and as crunchy as Midian's character creation rules are, I don't really use many rules during play.
I have a long-term project in the works to make a GM helper that takes care of some of the grunt work of running a game. It'll have time trackers, weather charts, and tavern generators. The end goal is to make something that can--by random rolls or via server-run program--can run the game world for me.
Kinslayer, thanks for the extra advice! I shall add a GM-guide for running Icar the Rob Lang way [tm]. I am warey of making it sound too authoritarian, though. I think a good example of a game world that really props the GM up is by Paul Elliot. Most people don't know much about ancient Egypt and Persia but Paul provides all the feel of the era.