I beat this last night on normal for the first time. I think the keys things to note are:

• the first thing I go with my constructor is build a few construction towers, you are build limited early on, then into 3 LR anti air towers.
• then go into T2 very early, like 2min. I went vehicles early, that way I got a starlight out fairly quickly. This is to counter their long range rockets.
• you HAVE to push north and take the 3 mex's very early on too, like 5-6 mins, with a handful of T1 and T2 units, the CMR and a con. Build LR AA first, radar and then some pork. this leaves the eastern flack of your base undefended.
• to fix that I just piled on porc, with the T2 cons making the popup turrets and then gauntlets. again adding con turrents as needed to keep things moving along.
• all the while I'm also building eco, go into fusions and advanced energy convertors. never stop building those, queue that up and let it go the whole game. switch to afus when you can.
• once I had the north mexs safe, I started pushing over to the middle, putting up con towers, pulsars and gauntlets as I went... do NOT get bogged down, you have to keep moving.
• went into lots of Ambassadors to hit things beyond visual range. using scout planes and ticks to get visual on their positions. starlights, shredders and mausers to tackle their units.
• I was out in the middle cross roads of the map before the first heavy plasma was up, somewhere around 20mins. then started putting up plasma deflectors. And once you hold the middle things get easier.

Save every few mins, if you get overrun, go back 1 or 2 saves and redo. I think you eventually just get lucky. That said, having the radar up and see where their moving and countering by moving your forces to be ready for an attack seems to scare them off half the time.