Last time i did it, killed 1,6 million italians with 75k loss before WW2
Right now it's absolutely impossible to rush ports (this was the best tactic before).
Initially do not move to use as much as possible entrenchment bonus; just avoid being encircled of course. Slowly retreat to your capital. The AI is dumb it will not push very hard, this limitate the combat intensity (because AI shuffle a lot each time the frontline change, and only part of its army is fighting at a time), during the first months witch are the most critical because of your lack of equipment. You've got an 'elite' division, switch it to your regular template to dispatch it's equipment quickly to the frontline
Your very first research should be infantry equipment 1 so your new factory will start producing better equipment (but do not switch your initial factories from basic equipment), then production tech and infantry upgrades.
Your political focus should be getting some MIC, then CIC so you can at least trade some iron.
with PP, take infantry expert and defense expert for a juicy +25% defense asap. then free trade law because you don't have any ressources. Economics laws are useless initially (you don't build anything)
Like people said, when you're forced back to your capital
You can survive as Ethiopia in 1.4.2 trivially by micromanaging retreat between capital and adjacent city [...] constantly retreat reserves with low org).
I strongly recommmand to keep one border with France or England so you can trade. Personnaly I choose to hold 3 provinces
After a few months equipment situation should be better. You can begin to upgrade your infantry division, adding infantry batalions up to 20 width. Do not train new divisions, it's better to updgrades those already on the field
You can also switch your factories producing basic infantry equipment to artillery, and add support artillery, this will help a lot.
When you get veterans, a top general, better equipment and 20width template (about end 38) italian army should be exhausted and you'll be able to push them out of Ethiopia quite easily.
I recommend to go fascist, because you will need the manpower
edit - I did this one week ago