What you need to do is make a map with circular islands with enough hexes to have about 2-7 cities each, then change the sea color from blue shades to black shades.
this will mean the map is representative of space.
you can use gems and marble resource models in the water(space) to act like meteorites and gas clouds etc.
allow (space)ships to go over land as well as water.... this is for 2 reasons, 1 so that space ship yards can be located from towns not near the edge of the 2d planet, and 2 because ships can enter atmospheres and fly over 2d versions of theoretical planets.
next, instead of calling a unit a space marine, name it a legion, since during the horus heresy the marine chapters could have over 1000 marines there would be multiple equivalents of terminators (first legion) or scouts (tenth legion) etc.
pretend each unit is representative of 100 marines.
so when working out realism, you would have 10 thunderhawks as transport, as 1 tiles worth, could 100 marines take on 10 thunderhawks... maybe.
ships... as follows.
Work vessel, 10 mining vessels, per tile, farms space tiles early game
mining fleet, 50 mining vessels per tile, farms space tiles late game at 5 times the rate.
thunderhawks, 10 transports per tile, transports 3 legions of marines (300), 1 legion of terminators(100), or 2 dreadnaught groups (20 dreads)
Gladius Escorts, 4 escorts per tile, light attack, fast speed.
spacemarine strike cruiser, 2 cruisers per tile, medium attack, bonus vs city, medium speed, can carry 3 thunderhawk units
spacemarine battle barge, 1 battle barge, high damage, high bonus vs city, slow speed, can carry 9 thunderhawk units
Units as follows.
bolter armed tactical marine, standard unit, attack from 1 square away.
meltagun marines, good attack vs all, must be in same square to attack.
plasma gun marines, good vs heavy troops, 10% damage return, attacks 1 square away.
devastator marines, cant move and attack same turn, high damage, can attack from 3 squares away, can attack space ships.
terminator, slower speed, higher armor, higher damage. attack from 2 squares away vs non mech.
assault marine, attack in same square, move double the number of hexes.
dreadnaughts, high damage vs city, troops and mech, high armour, slow attack.
predators, high damage, high armour, 3 squares range.
vindicators, high attack vs city, 1 square range.
bikes, high speed, 1 square range, high defence.
veteran sterngaurd, higher damage then tacticle and double melee damage.
whirlwinds, high damage vs space ships and citys, 3 squares range, low armor
land speeders, high speed, low armour, good vs tank.
scouts, high visbility, good in terain, 2 squares range, higher speed then tacticle.
non combatants.
great general = space marine commander.
great engineer = techmarine.
great artist = librarian
great scientst = chaplain
workers = servitors.
settlers = civilians.
Tech tree:
Terra Forming(Agriculture, make food)
Mining (get steel from the earth)
Gunpowder (archery, access to basic marine)
Biotech (all troops gain 25% attack and hp)
Ceramics (construction required for inter planetary entry)
M: Carbonite working (marine defence increased by 100%)
M: Engineering (construct city defence systems)
B: Geenseed Mutation, (Tradition/religion equivilant)
B+E: Human bioelectrical interface (power armor, marines gain +200% defence)
C: Plasma engine (Sailing, create a mining shuttle)
C: Space time continuum (calander)
C: Alien Language (writing)
and so on... need more ideas let me know.
