Yes, the DHCRS might be quite hard to get used to it if you haven't played on one of my PWs, though it is only a very light version featured in this module.
Most of the things you need to know have been put into the User Manual.
I made upgradeable only the skills that are used during this adventure. So all skills are worth upgrading, Though some would be more useful than others, and it also depends on your character's Archetype and how you see your character.
Since the theme of the module is "War", upgrading Combat Skills is advised.
As for Social Skills, there is only Deceit that is available to upgrade if I recall well. It is used in only one secondary quest during a conversation, and only if you have managed to fool the guy with the Acting Skill first while wearing the bad guys outfit. (otherwise it goes combat).
It might not be worth sacrificing Character Points into that unless you really want to.
The Rogue Archetype starts with a higher value in those Skills.
**Some basic explanations:
- Upgrading Strength increases your Damage Modifier, and also your Attack Modifier with heavy weapons.
- Upgrading Stamina and Willpower increases your Wounds, your Healing Rate, and all your resistances (poison, illness, etc).
- Upgrading Agility increases your Attack Modifier with melee weapons. (except heavy weapons).
- Upgrading Awareness increases your Attack Modifier with ranged and throwing weapons.
- Upgrading Reflexes increases your Defense Rating.
- Intelligence and Charisma have limited use in combat.
- All Stats affect your Skills. (check the User Manual to see what Stats are used by a given Skill).
* Purchasing Advantages & Techniques is advised. Just read the descriptions and take what you need. Some are more adapted to a style of play than others.
* The most used Skills are:
- Combat Skills (depends on the type of weapon you use). Defense is only useful if you rely on a shield.
- Anatomy. Some of your attacks may ignore the opponent's Armor Rating.
- Medicine. When using bandages or herbs.
- Survival. To skin/forage for ingredients such as herbs and venom.
- Alchemy. Only if you want to use poisons.
- Stealth. If you want to avoid most of the fights.
- Locksmith, and Traps. Only if you are into that.
- Perception. If you don't want to step into a trap.
- Tactics. Heavily used during Chapter 15.
The other Skills aren't that useful.
- Riding. Only during Chapter 15, if you want to ride a horse and fight effectively.
- Lore. To study artifacts and learn more about their properties through the option in the Character Menu. (F12).
- Deceit and Acting. For one secondary quest only, and if you want to avoid combat.
- Athletics. You will run and swim a bit faster, and avoid some traps, but otherwise the Skill has no other use during this adventure.
- Craft. Used a couple of times only.
The setting of this module is supposed to be historical, with no fantasy elements included. (except legendary beasts from ancient myths of the time). So the magic system is not included, there aren't any spell.
I hope I have accurately answered your questions.
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Do not hesitate to ask if you need more input.