Hi David,
We sailed the east coast on our 40ft catamaran for several years and have many recommendations for you. Our range was from Newfoundland to the Carribean. I would first say you should learn what you can handle for sea conditions. The boat can typically handle more but it's the contents inside that decides where the limit is. So, venture out in different conditions and see how it goes. From there you can listen to the weather and determine whether it's a go/no go. And most importantly, DO NOT HAVE A SCHEDULE!
Maine is the ultimate cruising ground (I am heavily biased as I live here!). You can cruise the coast of Maine for a lifetime and not experience all of it and, you will experience nothing else like it on the east coast of the USA. Having said that, we would usually head to Nova Scotia for the summer as we grew tired of dogging the lobster pot buoys in Maine where the east coast of NS has none during the summer. NS is very close to the cruising experience in Maine but it lacks a bit in the majesty. September/October are the best months here we think. We would usually leave mid October to head south hoping that hurricane season had settled down (that didn't always happen!) If you can manage the fog, current, wind, rocks and pot buoys here, I would say you can pilot a boat anywhere in the world. Anchoring can be interesting. You will learn to love the mud as when a 40 kt front comes through, you will move no where. Cleaning it off from your rode in the morning won't be so hard knowing what it did for you the previous night! Pick up a copy of 'A Cruising Guide to the Maine Coast' by Taft/Rindlaub and it will tell you all about it.
Going south, what everyone else said down to NY harbor. Although, there is a great little anchorage at New Rochelle (N40 52.9, W73 47.3) to stage for the trip down the East River. The stretch from NYC to Cape May, NJ will probably be the hardest as Sandy did a number on the NJ inlets and I'm not sure what has been done to fix them. Active Captain may provide some better info. With no inlets available, it will be a 90 mile offshore trip. We did it several times as an overnight on our cat, just watch the weather and do not have a schedule (did I already mention that?)
From there it's up the Delaware and down the Chesapeake picking up the ICW in Norfolk. The Chesapeake is another great cruising ground you will want to spend some time in. Solomons Island was our usual base with friends there but we would try to spend a couple weeks in this bay on our way south & north.
Down the ICW, we enjoyed Oriental, NC, Beaufort, NC, Charleston, Beaufort, SC, Cumberland Island, GA, Miami, with many anchorages in between. Ultimate destination was the Bahamas which we hope to see again on our R27.
Feel free to contact us when you're up here and we'll be happy tell you more about what we know.