There's an old sailor's rule of thumb, 'never go to sea in a boat shorter then the seas you'll meet'. By this they mean if you're in a 20' boat and the wave train is 22' long, you'll be fighting a pitch pole event, which isn't particularly enjoyable, trust me. I've pitch poled quite a few boats, all fortunately were dinghies or multi hulls, but still not a pleasant experience. For those that don't know what this is, it's when the sea grasps your stern and flips you, end for end onto the deck. It often happens at sea when attempting to surf down the face of a wave and the bow digs into the back of the next wave, stopping the boat. The wave under the stern, then continues forward, carrying the boat with it in a spectacular stern over bow flight, until you crash down with the keel facing skyward. Needless to say it's hard of boats, equipment and ego's, not to mention your life.
Amigo is certainly capable of this trip, but it would be painfully slow and very uncomfortable. It surely would fit into the category of being too small for the seas, but sailed well, in fair weather you'd eventually make it. It would take over a month, assuming you don't encounter calms (very common on this trip if leaving from the west coast) and made hull speed the whole way (you'd be lucky to average 1/2 to 3/4's hull speed).
Pacific Seacraft's Flicka would also be a choice, a better one then Amigo, but again, not well suited for the same reasons, though you'd have standing headroom.
You'd want to take a boat as long as you can afford. The longer the better. Not for speed, but more importantly, comfort. I've lived aboard and been in open ocean many times and I can tell you a short boat is about the most uncomfortable thing to be in when in blue water. The motion can become unbearable.
If you had to do so, then choose a boat with a high D/L (displacement/length ratio) which will make the motion more comfortable. Also a design that has a long "roll moment". Gaffers are good about this, having less lofty rigs and lower ballast/displacement ratios, the roll moment is less "jerky", making for a more comfortable ride.
When at sea, the most important place is the galley. It has to function well or the crew has to eat "cold" out of cans. Being able to use the galley requires a "calm" boat. It's difficult to survive a passage and remain healthy if you're using "rations". It can be done, but it's hard on the body, mind and spirit. This is also part of the comfort while aboard. How many of use would be useless without the morning cup of coffee? I would and will experience caffeine withdrawal within hours if I don't have it. You can't make coffee in a pitching and rolling boat. Hot food is necessary for good health and body warmth after a spell at the cold, rain soaked helm.
I can't emphasize the comfort thing enough. We can "rough it" for a few days, a week, maybe two, but several weeks at sea, possibly constipated from the dozens of cold ham sandwiches and canned food, trying to use the head, that's bouncing all over the forepeak as the boat yaws and pitches is difficult to understand until you try it.
Don't get me wrong, several have made astounding voyages in absurdly small craft. The one that comes to mind is a fellow that crossed the Atlantic in boat that was shorter then he was tall. He couldn't even stretch out completely when he slept. He also had a support team following behind, just incase he wanted to give up, which is a wonderful bit of luxury, few of us can afford.
Me, I wouldn't consider it in anything less then a 30' boat, which would feel small to me, but at least the ride would be tolerable.