1. The problem with the hanging script bug might not have been so bad if the original design decision had been to eliminate quest items once they’d been used. (I’m guessing here, I have no idea how the programme for making these games works). Why did I need to carry round things like Baretta’s package, Civilia’s necklace, etc. etc. after they’d been handed over? It also meant that it was much more difficult to find things in the inventory because it was cluttered up with junk. Can they be eliminated from inventory in future games?
I dont think it would make a big difference, cuz there arent that many quest items.
But the answer to your question is: yes.
Why I kept them was because I did not want LF to be a mechanical game, in the sense that the game itself identifies which item wont be useful anymore and consequently gets rid of it. I wanted any item to be potentially useful again in the future. Kinda giving you more freedom than in most games.
2. Compared with other Aldorlea games, the LF series seems to have many more bugs, and some of them really serious ones. Is there something about the development process or beta testing process that needs attention?
They are simply much bigger....
3. There were several mistakes in the Official Strategy Guide, some minor, some more significant. Is the Guide included in the beta testing process?
Well could you please send me a PM with the errors and I can edit them?
4. The translations have improved immensely over the series, but there are still a lot of small things, for example (can’t remember the names of the NPCs, so) the guy in the Undead Guild should not “learn” spells to characters, he should "teach" them; the woman who gives the big rewards in the Arena talks about how many people “winned” – no such verb exists, it’s how many “won”.
Titaness is taking care of the proofreading but we finished the one for LF3 only recently so you may have played with an "old" version. Feel free to download the game again and see if you see differences now.

5. My memory may be faulty, but I think that in LP non-active members got a small percentage of exp points from fights (was it 10%?). If the LS trilogy is also going to have a big number of characters, would it be possible to consider using that idea again? Having to level up so many was incredibly tedious, even using the Lava Pool, and made it really heavy going at times.
The 10% thing wasn´t put back cuz it wasnt very natural, and IMHO it was possible to finish the game without grinding up too much, especially if you subscribed to 2-3 guilds...