So, I'll start with listing what I know and/or remember so far (the "unknown" points are actually questions from me, and the single dots are just for structuring the post by separating paragraphs a bit more) :
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* direct-fire weapons (or rather, the ai targeting-code for those) seem to be limited to about 30km, judging from my experiments (result: CTDs) with "planet destroyer" stuff ... I'd guess it's the usual Integer-limit of about 32700something (32767 ? *update* likely the same 32768 that Litcube mentions below */update*) in meters - if this should be in a script-file instead of hardcode, though, it might be increased.
Can anyone confirm if this is a hardcode- or script-issue (and, if the latter, which script file(s) are involved) ?

* the number of HQs in hq.xml is limited to something between 7 and 15 (result if with 15: buildtimes and ressource-requirements vanish, and shipbuilding doesn't work)
WRONG. I had a hard-to-spot typo in my hq.xml - By now I'm at above 20 HQ-types and counting... - Sorry for that misinformation

* the number of weapongroups in TLaser seems to be fixed, as far as I can tell (so far found no way to add new ones)
[update - JonfersonSDD] 32 weapongroups, fixed.
* sector sizes are fixed to about +-4000km in each direction (though it seems to me that planets and such can be placed further outward?)
[update - JonfersonSDD] 0,002 metres * 2.147.483.648 ~= +-4.294 km
* [JonfersonSDD] player account is limited to 2 billion (= approximately 2^31)
[AP-related question: I know it was raised for the player account in AP - but does this lead to an increase in max. ship/station/item-price

* turrets are NOT limited to 12 guns - as far as I can tell, only the weaponsscreens' mounting function is; and I already have scripted a small replacement-weaponsscreen recently - Release-Thread.
I somewhere read there are 2 different types of gunpoints - of which one scales up quite well while the other doesn't. It had something to do with visible gun models and such, but I don't remember exactly what the point was...
* ships are said to be limited to 6 turrets plus the main bank - but since I only recently got to learn .bod syntax, I couldn't yet test myself if the sideeffects of breaking this limit are more than the abovementioned weaponsscreen-complicatiions...
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* max. number of TLaser-/TBullet-entries (didn't count, but I added quite a few - maybe 15 or 20 in addition to what MGM 4.8 has)
[update - Litcube] 32768 max. - for all TFiles each
* max. number of ship entries in TShips so far (~1100 shiptypes and counting...)
[update - Litcube] 32768 max. - for all TFiles each
* unknown: max. number of starts (I currently have about 20-30)
* unknown: max. size of ship-/station-models (both in meters and polycount)
[update]
* unknown: but PRESENT - max. number of jobs running (or maybe it's just because they produce too many running scripts?? Then, my total running script count actually went DOWNward from 20k to 18k) ... I lately bumped into that so often, it really gets annoying

Please post all limits you know of which are missing in this list, thanks

I'll now and then update the first post by quoting what others have found, to keep it a comprehensive list, as intended (though intervals might differ...) .
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