Pentax K5-II

Good Morning

I am just beginning my journey of upgrading cameras and entering the world of SLR from a Bridge Camera.  I do not have much experience with photography and am looking to expand and develop my interest.

Currently:

I currently have a Fuji HS20 which is approaching two years old and whilst I find it an excellent camera it is very lightweight and as I have 'larger' hands and fingers I find the zoom to be a little tricky at times, so am looking at upgrading to DSLR.  Additionally my Fuji seems to be finding a new home with my mother more and more.....

The types of photography I do at the moment vary from holiday snaps which is mainly focused around mountain scenery walking in the Austrian Alps.  On the flip side I currently run a shipping website for my hobby and would therefore be using the camera out at sea frequently.

One of the things I liked the look of with the HS20 was the really long zoom however I have not found myself using it as much as I originally thought.

Future:

My leaning towards the Pentax is due to it always being the preferred camera of my late father and the fact that it has acti-shake built into the frame something that really is needed when out on moving seas.

Lens wise I am very open to advice and thoughts, I am looking at at the longest circa 300mm lens.  Having been reading around Nikon, Canon etc they mention a 1.6 multiplyer on the lens zoom is this some the Pentax has also as I have not found any info as yet.

Are there any negatives of having a body with anti-shake and also having a lens with it in also?

Apologies if I sound a numpty but I guess everyone has to start somewhere.

Thanks

Paul