Hey there!

A few questions about preparation and creating villains:

1)
I wondered how you make up the NPCs, do you make them add in advance or think on stats & perks and flaws on the fly?
I found it to be a lot of work to build a group of NPCs with suitable equipment stuff and stats.

Though, I suppose I have to do this at least for some of the main villains.

2)
E.g. I want to add a group of individuals who should hunt the pc's. And they want to take it slow, e.g. frighting one of the pc's while he alone so he gets frighted and runs of to the others, just so the next trap gets triggered.... Of course I will do my best not to reveal the whole team of villains just yet.

I have difficulties estimating how powerful i need these guys to be. In the player party is currently just one mage who has high skills in mind control and such things. The karma level is pretty low, but the player is experienced and iam not. Often he thinks of traps / possibilities that I didn't dream off

Later on - or so I planned - is that the players should attempt on their side to track them down individually and set a trap on their own for them.

There are both the sample grunts and, for runners, the archetypes in the book. For a quick NPC, just grab one and tweak it a bit. I would definitely recommend at least jotting down some stats beforehand, rather than fudging the numbers. This is a game of quick one-shot takedowns that rewards lateral thinking; don't be upset if an encounter is not challenging as you envisioned it would be, or even if they breeze by several of them. Eventually, the players will either have bad luck with the dice, or not be able to think of a clever way out of a dangerous situation, and then there will be cursing of dice and spending of Edge.

Keep two things in mind. First, if you actually make the NPCs equal in power to the group, that is a 50/50 chance they will lose. Typical NPCs should look tough and/or outnumber the PCs, but actually be statistically a bit inferior to them, although there will also be fights where they either outclass the opposition (gangs, etc.) or are outclassed by them (Red Samurai, etc.). Second, if this group is attacking the PCs when they are alone and/or dressed for a night on the town rather than a night on the job, then they don't have to really be that powerful to mess up the group.

To be honest, I just wing it for the most part unless a confrontation is part of the plot.

For the most part, I wing it. For major NPC's, I'll jot down a few key stats, like their skills and equipment plus dice pools. However, I usually don't build them fully, I just give them whatever sounds right.

If you want something to hunt the party, I'd consider building an astral-based strike team. Get a hermetic mage with an ally spirit, a bunch of elementals, and a full compliment of Watchers. The ally spirit manifests and casts Invisibility on itself, then uses spells to scare and harass the team. If he's caught, he drops the spells, de-manifests, and runs away to the astral. If the team mage tries to follow, the moment he uses astral perception of tries to project, the astral attack pack dogpiles on him. Watchers aren't much of a threat, and medium force elementals aren't too bad, but since they all get the "Friends in Melee" bonus, the lot of them is really hard to take out. If your mage is smart, he'll shut off his astral perception so the spirits can't get him anymore, but then the opposition mage and ally spirit can escape freely.