Ofc, make sure you inspect any bosses or minibosses to understand what their new honour mode moves are.
The HM portal for Halsin's shadow-cursed land has very few HP compared to other modes, so be sure to get party members who have AOE attacks or a very solid plan, especially for the archers that run near the edge of the lake.
Since you know there is a killing Isobel check, also know that I was talking about inspiration in regards to an in-game contingency where if Isobel is alive as you get ready to leave Act 2, (at least that's when it was for me) there will be saving throws (14 wisdom?) to avoid murdering someone else you might not want to die. There is certainly a way to kill neither, I have done so, but bank inspiration in case if she happens to be alive. Don't use equipment giving disadvantage to saving throws. If you kill this second person and fail the following roll, you might be in a very, very, very bad spot.
The shadow-cursed shambling mound in Act 2 got buffed and so did Grym, some of my friends lost HM saves this way, so be sure you are well prepared. Shambling Mound fight doesn't yield anything indispensable so I might just skip it next honour run.
You can kill people from Moonrise towers by ''areas''- AFAIK, the prison area doesn't communicate with the main area, and the dock/outdoors area also doesn't communicate with the main area. Scrying eyes do alert to your movements, but there are ways of turning that to your advantage- I just kill them though. Z'rell is a pain in the hallway and can definitely be killed quietly in her study if you close the door and kill her eye first. Some guards, even in the throne room, can be lured in and killed without any issues. There's always the option to keep a party member in camp in case you mess up.
Shovel can be used to surprise enemies and to block poison vents if needed.
Kill the caravan absolutists before you summon the Drider if you want to side with the Harpers, but I'm guessing you might choose not to do that lol.
Unequip your weapons before the self-same trial if you have OP builds that rely on items, especially Lae'zel with her silver sword.
If you use a slow character who doesn't use ranged weapons, kick Shadowheart out of your party in Rivington, pass the checks, and get Ferg to sell you the Hellrider Longbow for +3 initiative.
If you're going evil anyway, you can bypass the end fight by simply detonating Gale, which is very very mean and not at all nice but also a great way of finishing HM unscathed.