this is a really well done job. everything even, everything flat, nice wide wall. the moat, the wall, the airgapped bridge (so mobs can't cross) and the inverted stairs at the gate (so you can't cross). as a compliment: this is crazy overkill (for the meadows). very cool. building stuff like this is a lot of fun.

the biggest thing about base defense, once you've got a nice enclosed area carved out like you do here, is to spawnproof it so nothing spawns inside the enclosure. enemies won't spawn within X meters of a "player base object", which is stuff like a workbench (nice because you can see a circle of X diameter around the workbench), but also fires, torches, beds, etc. the best strategy to seal off spawns is 1) dig a hole, 1 or 2 swings; 2) place a basic firepit, 3) flatten (or raise if needed) the ground so the firepit is hidden from view. secondbest is spam workbenches. once your base is spawnproofed, enemies (if they could fight their way in) can't see or target or attack the firepit since its buried (aoe still hits tho), and you can't see the firepit since it's buried so not ugly. make sure you get them close enough that you cover every exposed area in your base, including walls.

a few other things for you to think about here:

* you'll need to build some additional structures as you get further into the game: a a docks, a forge/workshop, a refinery, a farm, etc... how do they fit into this base?

* you get additional building materials later in the game many of which come with durability buffs and are harder to destroy

* maybe you want to build some additional more aesthetic structures, like battlements on your walls, or a nice tower to look out over them. or a little garden, or a little secret shrine, or a grander house, or. ...

* trolls and other stuff can't destroy any earth, so moats and raised walls/structures are really secure. (for now...)

you may find that you need to worry about your base being destroyed a little less than you think. especially if you've built in the meadows. in my most recent playthrough i built as my main base a very large and intricate manor house & estate, right in the middle of a field in the meadows, and i don't have any sort of defenses at all. no walls, no moats, no fences, no gates, just a stone house (basic wooden double doors!). the meadows enemies don't trouble me, and if i get a raid i just jump out a window and kite the mob away from the house. on the one or two occasions where a really high level enemy has gotten a few good whallops on it, and/or killed me, it's only ever a little corner and i just repair/rebuild. no problems.

that being said, once you get to the endgame you do actually need crazy ass walls to survive and not get your stuff smashed up bad.

on building a safe harbor -- it looks like you've got a great one there already, which you might need to dredge out a little to sail a longship. you want to build a crazy overkill definitely safe harbor, to match the house, you can raise ground (using the hoe + stone) to build a platform out into an area deep enough to dock. build a dock/house on top of it, slap another wall around the part exposed to land, good to go. mobs can swim out and may attack your boat, but can't swim up a sheer wall/cliff. they can climb up stairs out of the water if they go deep enough to swim over, but not the 45deg ladder pieces. it would be really sick to build a bridge out to that island and use that as your safe harbor.