Mission 5: Forget about that captain whatever to tell you use missile, IGNORE HIM. Build 2 outposts you will be fine. Stock up resources using outpost to generate manpower, when attack wave come push out tanks from both of them (if enemy only have air, use rifle to defend instead).
Mission 6: Watch the enemy units, and remember the ROCK PAPER SCESSIORS (practice in quick play hard-hard mode) First ring: rifleman > scout > tank > rifleman Second ring: MK II > air unit > sniper > ground units Third ring: roman > sniper > tank > roman
Tank is the counter to mass ground units MK II is the counter to mass air units
Roman is an excellent unit to absorb damage, allowing your more expansive units (tank, MK II, nighthawk, queen) to hail down the enemy.
I beat mission 4-6 using massed Grodetz, but by the time I have enough supplies and buildings to mass them up the enemy has already attacked. I use this time to mass up my supplies and spam marines/romans. After the big rush the enemy is extremely easy to take down with at least 6 Grodetz. Personally I found 5 to be harder than 6.
I only just done it lol, I done as you said with 2 outposts, I already ignored the Special Operations Base, but instead I would spawn heavy amounts of marines if there was 1 tank, alot of marines and aircraft, I had to last a while before I upgraded my outpost, from there on out I spammed the Bi-Walker unit, Groditz I think it is called...
Mission 5 is so strange that it seems impossible to defend if you EVER try to use missiles as suggested, the mission briefing and instructions are totally ridiculous for this simple fact. How this mission could ever passed beta testing need to be questioned.
You can build missiles while making troops like the black queens or you can make the long range snipers and the prides for mission 5 and when the AI says that he will protect me he didn't coz he just made at least 10 scouts then done so i had to take matters to my own hand
I used missiles in mission 5 and I beat it fairly easily. Of course, I built units as well. I can understand being stuck on mission 5 if all you built was missiles, however.
Bank, ops, set on influence, outpost, use marines and tanks accordingly, if you get enough resource send a couple of missiles. Make pride when enough influence. Prides own all tier 1.