[@Corrovax] One of the trickiest parts of DMing solo games is that most Tabletops are built around teamwork. In a solo game, you need to rebalance fights around a single party member, ensure an unlucky roll isn't the end of the campaign, and perhaps sllow some extra abilities or items (like allowing them to cure as a bonus / swift action, or make their potions twice as strong).

I would probably suggest OpenLegendRPG.com for a simple system with wide versatility. The game is designed around not punishing failed rolls as harshly. It is versatile enough that nearly any scenario can be created with it. The biggest issue so far, asides from being fairly new, is that there are no enemies created. On the other hand, there is a generic enemy template that can be modded / tweaked with a little effort to do whatever you want. The plus side is that you don't need to spend hours prepping encounters. The downside is that you may need an externsl resource to model your enemies after.

I suppose a question I should pose to you: are you planning to run this on the forum, in PMs, or live through Discord or some other chat program? This greatly affects the ease of the campaign from both ends. If it's PBP, you have more time to think through your end of things. When it's live, you have to think on your feet and have a lot more prep done.

Lastly, I feel like you could combine most or even sll of those story hooks into the same game. A magic-imbued hitman / ghost hunter who destroyed an artifact on the job. Now on the run from whatever's after then, mage-hunters, and a previous job gone bad. Just a thought. I like to keep options wide open in Tabletop games.

I can't say I have time to express interest. I wish you luck, and if you don't get many takers here, you might try the Tabletop section. Probably net a different demographic there.