Welcome to TBN!
My first thought is if you could provide a bit more info it would be helpful....will you be removing numerous whole trees...stumping...or just thinning and hogging....do you want it to be done quickly, or pick away at it....
a 50 HP tractor w/backhoe will not be cheap, particularly if you are looking at a new machine. In my opinion, perhaps a bit overkill for the 8 acres, and possibly a bit big for "landscape" work, depending on your definition.
Is the backhoe primarily for the postholes? BH's are expensive options, a PHD is much less expensive.
Are you moving whole logs or pieces? I use my forks on my 32 HP CUT to move multiple 8' logs around versus whole trees, easier to maneuver/stack.
For getting the job done quickly, you could consider renting equipment to remove trees, again, if there are a lot to remove. An excavator is ideal for this, you can push the tree over, fill the hole in, and move the tree to wherever you want for processing. Much Much quicker than a backhoe on a tractor....trust me!
Having said all that, if you're retired with plenty of time and want to play, you could certainly do it all with a tractor/BH.
I would think a 30-40 HP machine would work well for your application...again, jmho!
I'm sure you'll get some great feedback from more TBN'ers....
Good luck!