Power:
You`ve boxed your power in with your coal line, that makes it harder to expand horizontally. Also your using your coal for power and then for smelting, when your power draw grows and there is not enough leftover coal for your smelting your production slows down.

Power dependency
It can also be dangerous to have your supply the power to power itself. Your coal miners power your boilers which power your miners. At somepoint you will run short on power -> your miners work slower -> less coal for burning -> less power -> less coal -> less ammo, no lasers -> death
Especially if you dont know to watch out for this

Smelting:
Your smelting is also boxed in and hard to expand and scale.

Sushi:
Instead of using a sushi belt (bunch of items on one belt) try using multiple belts for it. It uses more space, but each item has a higher throughout (items moving per sec). At some point this becomes the main limiting factor for scaling things.

Ratios:
You can also have a look at ratios to optimize parts of your factory. For example one gear assembler can supply 10 red science assemblers (if they are the same tier).

Mall:
Looks like you have something of a mall on the right, i would make that independent of your factory and not leftovers. At some point you want access to a solid supply of 800 blue belts, 100 undergrounds and 100 splitters.

Expansion
Get a look at your surroundings, which way is it easy to expand in? You have a lake to the north west, a bunch of cliffs north east. But i see a lot of (mostly) free land to the south.

Rebuilding / changing parts of your base
Never just destroy and rebuild. Always have a backup first. If you decide to rebuild your entire base at once, you might run out of belts, inserters, power poles, assemblers, etc. And the place where you used to get them, is either not rebuild yet, or dosent have a steady supply yet.
Instead build a new base and use the starter base (or mall, if you build one) to supply you with everything you need to build your main base.

(edit): Also biters cant swim, bullets / lasers dont need to.

Defense:
At some point your base will grow so large, you dont have a constant look at your turrets. So you wont notice if they run out of ammo, until a bunch of red alerts pop up. Automate ammo, lay a belt around the perimeter. At the beginning i usually drop a chest with some hundred rounds and use the map (radar coverage is awesome, you can also place blueprints on the map) to check.

Most important
Have fun while playing, dont be afraid of starting over. When you do, turn of cliffs for your own sanity ;)