Ya know, that is a great question! My wife & I had the same discussion when we went from the 232 Gulfstream to our new to us 300 Marlin. I was asked the question a thousand times by my Mermaid...."is this boat too big for you to handle alone?". So....we now have nearly a full season under out belts. And here are my thoughts. When everything is going well.....No differences. When $*#*%& hits the fan like last weekend when my anchor/windlass tried to pull up an old mud filled lobster trap.....not so much. lol.
Docking, and close quarter maneuvering is more of just the "learning curve" sort of thing. Perhaps a little more forward and prep thinking regarding getting dock lines ready, fenders in place, etc. The weight of the boat is a game changer. Horsing the Gulfstream by hand at the dock if needed was a breeze. Not so much with the weight/inertia of the Marlin. because of that, the honed skill of close quarter skippering is magnified with a larger heavier boat. I've been forced (a good thing) to become a much better pilot.
The answer to the Mermaid back in May....."no problem, I've got it". The seasoned answer.......a lot of practice at the dock when no one was looking (getting used to the bow thruster was actually a lot of fun) and plain ole experience. Now I can say honestly, "no problem".
Back to the anchor in the lobster trap calamity......I had to pull alongside a 60+ ft. multi-million dollar sail boat for assistance (I was alone on my boat). Came along side like a pro. He commented in an understated sort of way...."nicely done". I was a nervous wreck.
Short of it I think. Practice and getting intimately familiar with any size boat in good going is where it all starts. Honestly, a previous poster commented that as long as the logistics of getting from the helm to the dock lines, etc remains the similar...go big. The devil is always in the detail. Anyone can pilot a 100' motor yacht in a straight line in good conditions. In a harbor.....its a You Tube video in the making.