I thought that the Charlatan (half mage/half rogue) is the best class choice. He has all the necessary buff/healing spells, which is nice, but also fencing. There are a couple special, class specific, rapiers in both games that have great +wound potential (and thus, I think, make up for the magical shortcomings of the class), plus the Charlatan has a bunch of special moves that inflict guaranteed wounds. Just be sure to use the advanced editor at the start to strip him of all his useless skills and only invest in fencing and enough magic to just do buffs and healing.
I think maximizing your party for wound potential is the best way to play this game as it means you can cut through most trash mobs pretty quickly by mid game given that 5 wounds equals an instant kill. Set up your Elf ranger as a ranged fighter as bows also have maximum wound potential. Following this, obviously, only choose the special moves for all character classes that inflict wounds. Then get a tank for aggro and that's all you'll ever need. Magic sucks in this game except for summons, so having a ranger/elf with a summon is powerful enough to basically give you a fourth character (they don't do lots of damage, but they can take tons of damage). While your main charlatan/rogue can learn healing spells to use when necessary. Only problem is most bosses are wound resistant, which sucks, but I don't remember having much of a problem with this. Everything else is much easier, though. I was able to do the one on one cage fights in the opening city of "River of Time" way early just because it's so easy to kill non-boss characters with wounds.
Also, you don't need to invest in alchemy for your main characters. Just use one of the extra characters for essential/non-essential skills like arcane knowledge (for identification) and all the crafting skills (for potions and crafting). You don't need those skills on any main characters. River of Time only has a few extra NPCs so you will have to decide form the start who you want to use as a dump stat character (since I was a charlatan, I'd just use the rogue), but "Dark Eye" has a bunch of useless extra NPCs so there's really no worry there.
These games were just the right difficulty for me. They were hard from the start and stayed hard, but never frustratingly so. Like, I remember a plant boss fight somewhere in the middle that kicked my ass at first, but eventually was so satisfying once I figured it out. And I loved the scarcity of health potions. There are barely any health potions in "River of Time" (like under 20 in the entire game? can't recall but it wasn't much) and they were really expensive. I actually had to go gather herbs for an hour or so to make it through a really long boss fight towards the end and I can't remember the last time I had to do something like that in an RPG.