Im looking to buy my first telescope since the little one i had as a kid to look at the moon.
Whats the minimum magnification and resolutions needed to see details of planets (mainly mars, jupiter and saturn)?
In a 6" scope, Jupiter and Saturn usually look at their best at around 150x in my experience. Mars, being a lot smaller, needs more magnification - around 250x - but you need comparatively good seeing to make viewing at that power worthwhile.
I have a cheap little Bushnell 525 60mm (has 525x max magnification). The small field view makes the maximum magnification IMPOSSIBLE for tracking fast moving planets.
On lesser magnifications, I can make out stripes on Jupiter, several of the moons and blurry features on Mars.
In my opinion, for planet viewing, field of view is far more important than magnification.
'Resolution' is the parameter to be considered to see details (resolvability) and not magnification.
R" = Resolution (in seconds of arc) = 4.5 / Diameter of Objective in inches.
Depending upon the object (Mars, Jupiter or Saturn) you may decide the R". Data for these planets is available in Wikipedia.
I suggest you join an astronomy club or at least go to a couple star party's and see what you like.Most clubs have loaner telescopes you can take home once trained.Here is a link to clubs-
A good telescope for dso's(deep space objects) is the reflector type and the easiest to use and set up is a dob,(Dobsonian mount).To get a telescope that will give you views of Galaxy's,nebula,clusters and such you will need at least 6" aperture.
This is a good place to do some window shopping-
I have 2 of their telescopes a Starblast 6 and an XT 10-I love them both.
Thy really stand behind their products.
Stay away from e-bay and department store telescopes.