Update 1: Organization
Most of the first update (in fact the first few updates) are going to be of the housekeeping variety. I'll explain a few of the points that may not be clear in the screenshots, and I, and I'm sure others, are willing to answer any questions you have.
First, a look at the front.
Now, it's impossible, and in fact won't be necessary, for Poland to guard the front from both Germany and the Soviet Union. The Soviet Union should mind their own business until 1941, I hope (assuming I get that far), so Germany is the clear and present danger.
The tale of the tape will be as follows: They have about twice the base manpower (with numerous events that will increase that even higher), three times the base IC, and four times the base leadership. They have far better leaders (with numerous 5 skill commanders such as Rommel), and will have far better technology come the war to boot. Basically, we're up against it. Our one advantage is they are going to have to devote a lot of resources to both the front with us and the front with France. Also, Poland obviously has much potato.
We have a deficiency in Rare Materials, so trading with the Soviet Union is a good way to make up for that. We are also short on crude oil, but since our forces will be primarily infantry, we shouldn't be using much fuel. If we are lucky, we may be able to pull off one full armored corps for a bit of an offensive punch by the time war comes, though.
Ethiopia lasted all of two months... not a lot of shock there.
We got a few shitty events in pretty short order, but the only real consequence was we lost 2 national unity.
A look at our Politics screen. One advantage Poland has from the get-go is they already have pretty good laws enacted, and with spies lowering neutrality internally, you can get the Three Year Draft law on the second day of the game (which is the best peace time draft law... Service By Requirement being the best overall).
Also a quick look at our techs. Our focus is going to be mostly on infantry and land doctrine techs, with a few in armor to open up medium tanks, as well as a bit in Industry to give us a bit more IC. The IC difference won't be a huge factor, so we won't use more than one leadership point at a time on it. Poland also can't afford to waste time researching techs ahead, so after the first Infantry techs cleared, we shift to light armor. For land doctrines, we are focusing on the ones that benefit Infantry Organization and Morale, as well as the one that lowers delay time between attacks.
For production, right now, and for the foreseeable future it will be three brigade infantry divisions. We'll need quite a few full corps to fully guard the border, and even more to be able to counterattack and go on the offensive. Our manpower is very limited and will likely be the bottleneck that will force us to turn our focus to armor a little later on.
After reorganizing the Order of Battle (which seems beyond fucked at the start of each game no matter which country you play as) and placing our forces along the border, another look at the Western border.
And a look at our production. As of right now we have exactly enough IC to not be in deficit for supplies, Consumer goods, and the eight divisions we're currently building. Oh, and there's another disadvantage that Poland has to Germany: At the start the infantry practical is pretty low, with a -12% modifier on IC and buildtime. This is pretty different from HOI2, where making serial runs was a pretty smart move. It strikes me, in HOI3, that serial runs are inefficient, because I believe they use whatever the practical was for the first run, and don't benefit from its increase. You're better off manually making parallel runs as each clears for the maximum practical bonus, which can end up saving you a lot of IC. Luckily, with the rate we're going to be churning out infantry, the infantry practical will be pretty high as time nears. After one run of infantry it already increased from that -12% to a positive 3%, and each run will steadily increase that.
Also, especially in peacetime, always build Reserve units, as regulars will cause your consumer goods needs to go through the roof, as well as costing almost twice the IC for no real benefit. Mobilization takes about a month (give or take), so if you know roughly when the war is coming, there is absolutely no downside to building reserves.
Anyway, at least from an LP perspective, the first few months of HOI3, while incredibly crucial to your overall success, are boring for a spectator. So, to send you off with high spirits, I will leave you with some lovely images from Polish culture... so you know why we fight!
And that's about all I can think of.