I recently bought the game and finished Vesta Overkill mission today. I have now 3 missions left until the end of campaign.
You actually have 5, and while VO is the most (in)famous one for its challenge, the missions afterwards are arguably more fun as they require combat AND extensive orbital manoeuvring in deep gravity wells, while VO can be cleared with just a station with some launchers tacked onto it built specifically for this mission (also, VO lags like hell because of Cutter firing its 60mm cannons indiscriminately).
Well, unless you have some fully realized ideas for a custom campaign (I don't but would be happy to contribute designs and individual mission ideas if you do), the best way to use level editor is unfortunately hoping that someone makes a good (and working) custom campaign.
Fun with ship editor is easy - you have some cool concept and then try to make it, later to test it in the campaign and/or sandbox.
Module editor is more difficult, because tweaking variables is a bit dry. You can still use it to make components for your custom designs, or implement complex payloads/missiles/drones and their launching method, although I must admit that recently I have made some fairly interesting (as in the biggest is in 200MJ range, with 1kg slugs) heavy railguns and their guided nuclear/kinetic/flak derivatives. I have also started dabbling in a conversion kit of sorts - components you could just swap into a stock module design and have them work right away.
For me a lot of fun is designing what I perceive as cool ships, typically highly manoeuvrable ones, often trying to squeeze the most out of stock components - for example I can currently do Vesta with a
4kt 100% stock module corvette (NOT a mission specific ship, it has mission envelope in line with stock designs and,
with some extra drop tanks matches stock Corvette in terms of mission envelope, cost and mass budget) without launching any missiles or drones on intercepts; I have a 100% stock module gunship and frigate equivalents that can take on stock counterparts at 10:1 numerical disadvantage, etc. - or limited power - I have recently made a bunch of custom ~700t skiffs with power in 800kW range equipped with direct fire missile/torpedo launchers that can lay waste to large numbers of much heavier ships; some time ago I have also made a
stock powered drone (roughly Hellfire equivalent, but at half the cost) capable of soloing a Gunship.
I have also created
a bunch of much stronger rough equivalents to stock designs using stock modules.
I also like making stupidly high velocity intercepts* and having a lot of dakka** happen but I am easily amused.
Oh, and gratuitous overkills***, mustn't forget gratuitous overkills.
Lastly, you can search for any thread with "challenge" in the title on this board and have a go at that.
I am not really a fan of mods, CMP is mostly ok, but still has some minor dubious stuff, future materials/fusion/graphememe anything is basically attempting to do stuff way out of bounds of CDE simulation, and also a bit like modding blasters into a WW2 war game.
There have also been tournaments where people submitted designs and had them fight each other, but lack of multiplayer and AI limitations hamper meaningful comparisons a bit.
Nice, I like the use of orbital manoeuvring and high velocity intercept.
When I first unlocked ship editor, I never looked back to the stock designs.
My first (and a bit of a flagship) design was modified Laser Frigate equipped with a lot of 60-100MW coilguns as primary weapon, which quickly grew to Gunship size and was first used to beat Main Belt Extraction (I have later beat MBE with default fleet, but it felt very ineffectual). Over time it gained, then lost partial armour, Methane-Oxygen "afterburners" and vernier thrusters, gained concave, polygonal hull (changed base polygon twice), changed armour composition several times, was redone several times, customized, then restockified, and rebuilt over 2 patches.
It is now known as "Dragon" class gunship, available in several flavours, and is the Gunship equivalent that can chew 10 Gunships at once I mentioned above. But going to Vesta, I first beat it with a custom 6kt frigate (I since then scrapped and replaced, although it wasn't a bad design) mixed into remaining 7kt of default fleet (I think Missile Schooner, Beamcraft and carrier). I didn't really go well, as I lost the carrier, my frigate got gutted, missile schooner got mobility killed, I managed to stupidly get Beamcraft killed as well (IIRC after I sent it to finish off mobility killed Cutter), and in the end finished it thanks to zombieship trick (remote control modules installed on my frigate) - gutted, de-crewed frigate controlled from tumbling schooner, flying around shooting things (I no longer use zombieship trick as it is arguably cheese, but it still felt quite intense).
This included moping up orbiting Devastators as well.
Hope you don't mind me using your thread to pimp my stuff, but it is a good example of how I have fun in CDE.
*)
**)
***)