for single player.
Search settings.cfg and turn almost every "true" to "false"(including asteroid dynamic physics, simulation, etc),
set sector sizes to something large (to avoid loading/unloading sectors so often, even if more can be in each sector)
set planets and asteroids to small values.
set npc factions per galaxy to zero, turn length to -1, etc.straight delete the NPC faction config files and NPC faction folders(throws console errors, but disables them)
manually set your textures to the 64 pack in the config (it usually fails to properly set it, and still uses 128 even if you select 64 in the game)
open block config and disable animations for shields, power, etc.
You may also consider running the SP server in "battlemode" or "personal sectors" to just straight chop-off the extra frameworks.
You'll be left with a fairly barren galaxy but you'll be able to build in SP. If you can't get FPS in multyplayer, the manual settings of texture pack might be your bet, you can also set java to "above normal" or "realtime" priority in the task manager of windows(ctrl+shift+esc, may cause system instability aka B.S.O.D.)
You can also go though task manager and "end process" a bunch of whatever bloatware you have on your PC to free up memory and cycles (antivirus and firewalls are top priority here, they tend to screw over programs on low end systems by making execution take extra steps.) Some of that may need you to run msconfig (winkey+r, "msconfig", enter) in selective startup mode to disable "stubborn" things like adobe update, etc...