Thanks as always for the mod, and I definitely can (and do) edit my own milestones. :)
1) I wasn't able to find an "extended option for megabases" for the vanilla setting, as mentioned in the description. Is that just something I missed, or should that be changed in the description too?
2) It's "very early game" as in "second or third tech you will likely unlock". The thing that honestly made me want to include this is the fact that there is a milestone for a single silicon - which is just stone bricks, and with Aluminum installed, even earlier! Additionally, you have to make aluminum before you have copper, and there's already a milestone for aluminum plates! (Maybe aluminum alloys? :thinking_face:) And yeah, asking Brevven is probably a good idea - they'd have a better sense of their own mods than I do, of course!
4) Code that automatically detects and adds milestones for any science packs that don't already have one could potentially be a good thing to add anyway, as long as it can be assumed that 1) there is a reilable way to detect what a science pack is (do bob's modules count, for example?), and 2) the addition of said milestones for packs would be .. well, an actual milestone (again, do bob's modules count?) I'm a relatively novice modder, but if you have interest in this feature, I can give it a shot and see what I can contribute. :)
5) I'm specifically not using bob's plates, as I'm using ones provided by Brevven instead. I approached which Bob's mods I include in this playthrough by looking at each and deciding "does this mod add something I'd want to use even though I'm already using full BZ?" This is why I was wondering if bob's could be approached as an addon if a full pack isn't found. But if you're interested, my list specifically includes only these bob's mods: bobassembly, bobequipment, bobgreenhouse, bobinserters, (boblibrary,) boblogistics, bobmining, bobpower, bobvehicleequipment, and clock. Like I said, I was going for more of an addon style and then ended up using most of them - but notably, warfare/enemies, mci, and plates are missing. I am still on the fence about adding electronics, and it's not yet too late for me to do so.
I also agree with your logic that spitter and biter go hand-in-hand, but I would argue that worms aren't necessarily the same. I am a usually-no-mob player, but when I do play with mods, I hunker down and build a big wall. Late-game, I pollute as much as I want and just keep the walls repaired - so it's actually a big deal for me when I do go clear worms (usually with artillery) because I don't do it often. And with bob's adding new flavors (acid, electric, etc.) I was on the fence about whether to include those. I admit I didn't realize bobenemies had a preset addon with the biggest three, though, so that was a miss on my part.
6) I am pretty sure it is possible to change the default value or preset based on presence (or lack) of other mods - I know some BZ mods, for example, do something based on "SE 0.6+ or not". That being said, I also don't know how to do it, but like 4), I could give it a shot if you wanted.
7) I admit I'm very much enjoying BZ mods, so planetfall's mods seem, to me, like a natural fit - it was their advertised interoperability with BZ that led me to them in the first place. While new, the mods seem to be pretty cool on their own! As for your request:
mod name: BrassTacks
items: zinc-plate, brass-plate
mod name: IfNickel
items: nickel-plate, invar-plate
Notes: Like BZ mods, if playing with K2 and/or SE, the mods will add their own enriched and ingot variants, just as BZ mods do. Not sure if that's worth a milestone or not, I'd lean towards no. And like BZ mods, the group would be resources for all of these.
8) I might recommend adding silicon (yes, internal name is slilcon) instead of and/or in addition to the silica when bzsilicon is installed.