I need some help deciding which power to get first. I read on another site i should upgrade blink first. and on another it said i should grab possesion first. please i need some guidance. BTW im lovin this game so much fun being sneaky.

I think it depends a lot on how you intend to play.

I tend to prefer the stealth/knock-out way to play, and so Blink and Agility are my two preferred early upgrade routes. An upgraded Blink certainly helps later in the game where some routes out of situations tend to depend on it, and Agility helps you jump higher and run a lot faster to escape out of view. Combined with the Stealth Boots blueprint found later in the game, it certainly helps to stay hidden and make escapes. I only bother with the first level of Possession when aiming for a low-chaos game - mainly to access places stealthily under water as a hag-fish! I found the second level of Possession only dumped me bang into the middle of a fight because the spell didn't last long enough and was very expensive on runes, so that's an upgrade I'll only make later in the game if I need to ride a Tall-Boy to the river or ocean's edge so I can escape unnoticed.

Of course, if playing the high-chaos route, then your upgrade options would more likely make the Rats and Wind powers as a priority.

Stop time is a must IMO. It can be used for both stealthy routes and deadly routes. Once it's upgraded you can use it to walk through a room full of guards and not be noticed, or just kill them all if you're quick enough.

Dark vision. So you dont get surprised by enemies when you run around a corner, also it shows you anything you can interact with that would otherwise be easy to miss.

I need to be a bit better at playing the game and moving about with the time-slowing. I slow it, then faff around trying to think what I should do next Dark Vision I forgot - yes, another important one, and a great way of finding whale oil bottles that are powering up those nuisance arc pylons etc

well i went for dark vision and its proved useful thus far.

My stealth runs involved Dark Vision II first, then Blink II and Agility I, but also saving up for Possession II. I made more use of Possession than Stop Time, but that's just a personal style. On the other hand, Stop Time fits better with an extreme pacifist, no KO approach.

On high chaos, I'm a big fan of Devouring Swarm and Shadow Kill. I'm terrible at melee, so I tried to avoid fair fights.

For upgrades, in both low and high chaos I take the crossbow upgrades first.

I like upgrading blink, then picking up stop time as some as possable, after that it just depends on how I'd like to play.

Low Chaos: Blink is essential, Agility as well, dark vision is worth spending a rune on. Time stop is nice, don't know if it's worth 8 runes, though.
High chaos: Rat swarm is devastating. You can use one swarm, combined with sword arracks, to destroy multiple attackers. Windblast is also pretty cool.