Good move.You''ll be very glad you have one!Especially for your sailing grounds.
I have my radar
mounted on a swing-out bracket next to the companionway like you were asking. Yes, you''ll be able to see it just fine and in the in position, you''ll be able to read it from inside the cabin.
Yes, you''ll see everything,cans, nuns,lobster pot bouys and boats.
I reccomend the array be mounted one third to one half way up the mast(sloop rig
) wiyh a two or three degree down angle.
A leveling device is good if you want one but you don''t have to have one.
Home Depot has an assortment of brackets that work fine and are much cheaper than the ones from West Marine etc. If you would like some info on the install,check back here.