I recently beat this mission on hard. Here's my strategy:
1. Build your base in the northwestern part of the starting area to minimise the distance to the Spice field.
2. Absorb the first two attacks. Then, rush the western Ordos support base and destroy their Barracks and Light Factory. Don't bother destroying anything else for now and rush back to your base to defend it.
3. If you don't have units left after the six initial scripted attacks, restart. You are going to lose in the long run.
4. Get two Spice Refineries right at the beginning, and a third Harvester after you get your arms factory.
5. Then, either build Combat Tanks or tech up for Rocket Turrets. I recommend vehicles backed up with a Repair Pad. However, retreat whenever Deviators show up.
6. Against the Saboteur, either build a cluster of Turrets, a wall, have a task force ready (the Saboteur is easily crushed), or place Wind Traps south of your important buildings.
7. After that, get eight or more Harvesters and build and army of Combat Tanks and Missile Tanks. Got for the Harkonnen first, then for the Ordos main base. Fremen can infiltrate the Ordos main base via a ramp in the south and destroy their Construction Yard.