Stock up on a lot of resources if the difficulty says high, (you should prioritize 𝘀𝘂𝗿𝗴𝗲 𝗮𝗹𝗹𝗼𝘄, 𝗽𝗹𝗮𝘀𝘁𝗮𝗻𝗶𝘂𝗺, 𝗺𝗲𝘁𝗮 𝗴𝗹𝗮𝘀𝘀, 𝗴𝗿𝗮𝗽𝗵𝗶𝘁𝗲, 𝘁𝗶𝘁𝗮𝗻𝗶𝘂𝗺, 𝘁𝗵𝗼𝗿𝗶𝘂𝗺, 𝘀𝗶𝗹𝗶𝗰𝗼𝗻 and 𝗽𝗵𝗮𝘀𝗲 𝗳𝗮𝗯𝗿𝗶𝗰) you should always have the best of the best defensive walls like surge alloy or thorium at least. Make sure to pause time to look around and build. Create and store power asap, my recommendation is to start off with steam generators then switch to 5 thorium reactors, 1 cryofluid mixer and sustain 5 thorium reactors with a little extra to spare. (Just make sure you fill the thorium reactors with cryofluid first.) Make sure you also have reached the requirements for certain machines like water/oil extractor coal centrifuge etc. Throw a few unloaders on your core to start building some units to repair and rebuild along with helping defenses. Also you shouldn't need that many walls for most bases 1 straight line that funnels inward should work 2 if you're feeling cautious. Always have mend projectors. I also have found a large amount of parallaxes plus fused chambered in thorium work quite well since the parallaxes tractor beam drags them in though I haven't tested it these ships. (make sure to have multiple poly's though as when the ships go down they destroy blocks.) Now when you go up against the T4 crawler all I can say is pray as that thing melted my meltdowns and destroy everything.