Search south of Ars Magicana for the cart, south east of the Dwarven Bread inn. The accident between the two cart drivers is unrelated, and not part of a quest.
Are you referring to Shrimpo? Someone approached and asked about him as you left the graveyard? If so, there are graves in the north east area of the graveyard, with inscriptions you can read (the names based on forum members in the original forum).
Spoiler ~~[color:"#27384A"]click on the tombstones in order so that the first letter of each name spells out S H R I M P O.[/color]~~ (highlight the text to read)
You need level 2 Lockpick to open the door in the vampire's cave, or level 2 telekinesis to use the lever.
Head west from where you got the gem quest, south of the quarantine area, north of the poor section graveyard.
You don't need to talk to Elrath again, just break into his house and poke around a bit for evidence.
Rescue Zandalor and let him teleport you somewhere to get your teleporter stones back.
Verdistis is a smallish city, with little fighting. You will get quests there requiring you to go to the Dark Forest. I think the game was designed to direct you to Verdistis after Rivertown, but I don't think it makes much difference. You can pick up some potentially nice equipment there which could help in the Dark Forest.
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