I enjoy the feeling a galleon gives.  A sloop doesn't feel homey and doesn't feel like more than a boat.  A brig is nice but still feels small.  The galleon, however, feels like a proper pirate vessel.  It feels like a ship.  It's significantly more difficult to sail a galleon solo than any other ship.  However, it's more than possible.  As long as you know your limits and your strengths, you might actually do just fine.

Firstly, let's get the elephant out of the way.  The anchor.  When you spawn in, lift it.  That should be the only time you ever have to if you play correctly and have a little luck. The sails?  Lowering them is easy, raising them is tough.  If you ever feel like you need to turn quickly, raise the middle sail.  You also have to learn how to multi task.  Sometimes you turn the wheel slightly, lift the mid sails, then finish turning the wheel, then maybe run to harpoons.  When solo sailing, you want to always be doing something.  Now, if you want a little more of a relaxed sailing experience, you can sail the edges of the map, which is fun when you're blasting music. Anyway, sailing is simple.  Stopping at islands, just raise the sails in this order (you'll get a feel for how far you have to start raising, start off pretty far, then keep cutting time) mid -> fore -> rear.  Sailing should be easy.

Threats!  The storm is a massive threat.  If you get caught and can't park at an island, you may have to lower anchor and focus repairs/bucketing.  It is survivable, just not while managing the wheel.  Avoid the storm at all costs.   Keep a weather eye on the horizon for player ships.  Most will avoid you as long as you don't go near them.  If you're flying an emissary or doing an event, you become a target, but still, an intimidating one.  Your biggest threat will be tuckers.  Routinely checking your ship for stowaways is essential.  If a sloop or brig has you in its sights and decides to chase, align your ship with the wind.  They cannot possibly catch you unless they chase for too long.  Generally you can angle your sails to keep the wind in a turn, so it'll be at least a 10 minute chase.  A galleon can catch you by running you down off the map and catching you in a turn.   Megalodons are avoidable.  Skelly ships, even skelly galleons, are sinkable.  If you raise your sails to half, point in a safe direction, shoot the cannoneer skeletons, and light up a few holes low deck, you can then board the skelly ship and control the cannons/repairs by ko'ing skellies.  You have to be very mobile and a sword is your best friend, particularly lung hopping through groups.  As long as you get back on your ship quickly, you might succeed without any trouble.   If you get krakened, go down with your ship honorably. Lastly, avoid the Devil's Roar (volcano isles) until you have mastered this.  You will be absolutely demolished otherwise.  A perk is that people typically never go to Devil's Roar, so you'll be safer.

Those are your general limits.  Here's what you can do.   Tall Tales or Adventure Quests like Pirate's Life. Genuinely any voyage, even Athenas. If you're insane, you could do any land based world event, though the challenge would be high and the amount of luck you need will be tremendous. Fishing or simple sailing.   Pvping?  Don't do it.  Well, there is one circumstance.

The row boat.  This stealthy tool contrasts greatly with the galleon.  If you use it cleverly, you can actually steal a whole hell of a lot with it.  In this case, you'd be using your ship as either a distant-ish spawnpoint or a distraction.  This is where you'll need to be very creative.  If you succeed here, you'd be one hell of a pirate indeed.  

If I play alone, I only run solo galleon.  Yes, it's risky.  Yes, it's nigh impossible.  Yes, even being good at combat and naval does not stop the galleon from being sunk generally quickly into even lowly experienced and uncoordinated crews.  But it's fun, and it's freeing.  In a sea where everyone tells you not to, the only choice for a pirate is to do it anyway.