Galaxy Forge will pop-up a templates box if you double-click a planet.
On the bottom left of that panel is a "use default" option which is checked by default. If you leave this checked, your custom template will not be used but the stock default template will.
Some entries have conditions such as planets owned by Minor Factions have distance and number boundaries that restrict them. If one of these conditions applies, nothing will spawn at your world.
If you bungle a typed entry in your galaxy file for a world's template (make a typo, leave out a line, etc.) it often will result in nothing spawning (though sometimes you can get an odd weir effect).
This isn't a complete answer to your specific asks but it's a useful aid and not always readily spotted.
Additionally, you can search through this and may find some specifics--though you'll have to do a lot of reading and searching.
I'm a little rusty on the fixed starting points--I'm not sure if I've just forgotten the proper way to do it or if it occasionally breaks. But in the planet entry near the top is a TRUE/FALSE option for "randomizeStartingPositions".
If I can get time to play around with it, I'll try to get you a more exact reply and hopefully some modding genius who's making maps all the time in their mods will come on and lay it out in the meantime.
Hope this helped some.