I've had a quick look through and will have a better look including your provisional rules when I get time, but good job, an interesting read and on the whole, I think my house rules and yours are broadly aligned. Link to my homebrew rules is in my signature.
That said…
Core Game Quest Order: Personally, I would prefer my own starter quest (but then that is to be expected!) but I agree ‘The Trial’ should be moved out, either to after Q4 as you have suggested or to the end of the GS pack to use as a grande finale.
Chests: I use a ‘loot’ rule which is pretty much the same as your rule. For chests where the Quest Map doesn’t specify their content I just prompt for the Heroes to draw a treasure card (which I think is closer to the original rules), but any Wandering Monster or Hazard cards are just a plain ‘nothing’
Turn Order: I agree with your comments but found that it can take too much time, depending on your group, to decide the turn order each turn, so I’m currently experimenting with a random allocation OR a ‘skip turn’ option where each Hero can choose to skip their turn and once all Heroes have skipped or taken their turn you go through the remaining ones in their usual order.
Movement: I’ve played with fixed movement and hybrid D6+x movement and conclude that the existing movement rules are NOT broken. However, poor Quest design, particularly in some of the GS quests, Prince Magnus’s Gold for example, give the impression that there is a problem. I’m against any ‘if there are no monsters on the map’ or ‘If no monsters are visible’ types of conditions as I think it leaves open an exploit, where a Hero takes the ‘fixed movement option’ when the conditions permit it, prior to opening a door on their turn when they have a good inclination that opening the door will reveal monsters but by taking the fixed movement option, they dodge any challenges caused by a low roll. Personally, I prefer giving players an additional action named ‘Rush’ which enables them to (still playtesting this) either roll an extra movement dice or move an extra 3 squares.
Multiple Attacks/Defence: I use a ‘split attack’ attribute to handle these for the likes of the Polar War bear and +1AD for Orc’s Bane. In the case of the latter, I see the normal single ‘attack’ / combat roll in HeroQuest is a simplification or abstraction of a more complex and nuanced ‘real-life combat’ in which multiple blows may be struck in combination with parries and similar so the idea of a two-attack rule makes no sense to me as any number of attacks against the same target would still be represented by a single attack/combat roll.
Large Monsters: Agreed
Trading Items: Open exploit warning here – Hero with crossbow shoots at monster with his action, then moves next to another Hero, passes that Hero the crossbow (free action). The second Hero then shoots at a monster with the crossbow, then moves next to another Hero, passes that Hero the crossbow and so on. Giving/Trading Items must be an action (at least for the giver)
Selling Items: ‘Cannot buy or sell potions that are not listed in Alchemist’s Shop’ so by extension you CAN sell potions that are listed in the Shop? Is that an intentional change to the rules?
Hero Rules
Dwarf: Giving any Hero a ‘free’ equipment upgrade in my view weakens the ‘acquire gold and use it to upgrade your equipment’ advancement/levelling system that HeroQuest uses, as it takes away one level, and they are limited enough as it is
Barbarian: your ‘enraged attack’ is similar to my own ‘battle rage’ but yours seems more complicated to use/track?
Item Rules
Shield: I think that works but it is very restrictive what is wrong with carrying a shortsword on your left hip, a shield on your back and a battle axe in your hands and having rules that enable you to switch the shield and battle axe in the right circumstances, or prevent you from doing it when say you have a monster in any of the surrounding squares
Hand axe: A recover throwing weapons rule that applies to Hand Axe but not the Dagger is inconsistent and what happens when you introduce another throwing weapon like a throwing disc, is that like a Dagger or like a Hand Axe, inconsistency adds more complications, one rule for all. An action that can be used to recover a thrown weapon even if you are several rooms away seems odd. Place a marker, allow automatic pick up if you step onto the same square, or if you search the area in which it is located. Your rule also means that throwing weapons can never be lost (unless you do it on purpose) which removes a risk and potential wealth drain. Check out my rules for an alternative.
Crossbow: Perhaps more complicated than it needs to be. Can a crossbow be reloaded when you are adjacent or diagonal to a monster, can a crossbow be used on diagonal targets, how many attack dice, if any, do you roll when equipped with the crossbow and fighting an adjacent opponent?
For example: I’m equipped with shield and crossbow, I shoot at a goblin, who survives, I then move adjacent to the goblin, turn over, goblin strikes (I get one less DD), but has no effect, turn over, can I use my action to reload the crossbow, but then I can’t shoot it, or do I attack with my unloaded crossbow in close combat, how many AD, or do I just stow my crossbow and draw a sword, all whilst being adjacent to a monster, then attack with my sword (or same example with a battle axe?), if so then do I need to remember that my crossbow is unloaded and at some later point equip it again to reload it, before stowing it again, can you stow a loaded crossbow?
Monster Rules
The Yeti: Using a ‘lose 2 BP unless you can roll shields on 2 combat dice’ is a weird rule, it isn’t the usual combat process, it isn’t a ‘assume 2 skulls then defend as usual’, why a fixed 2 combat dice in defence, does it make any difference if you are wearing armour or drink a potion of defence or have magical armour
Ice Gremlin: Complicated but then I’m not sure off the top of my head what a better solution would be!
I’ll review your optional rules later when I get a moment and maybe also adds some links into this post to point you in the direction of threads that relate to some of your house rules so you can read the accumulated wisdom already espoused on such topics or failing that rehash the old arguments
