There is sometimes a bug with PLs. Before you buy PLs save the game. As soon as you get them, check your production queue to make sure they look normal, otherwise reload and try again. What i find works is this. When you want to buy a PL the first thing you do before even picking the item is move the slider towards 0 $, then pick the item, then pick how many you want, THEN start to move the slider, adding $ until it seems likely theyll say yes. This seems to eliminate the bug usually. IF, I say IF when you move the slider to 0$ it still says they will sell you the PLs, its buggy, get out of it wait a day and retry the steps above. Also if your in the Axis compare Germany and Japan, often Japan will sell items cheaper. Japan will train the Forest tech before Germany, so if thats something you want (if your buying INF), and believe it or not Germany usually has better CLs early on. Leave your troops alone, theyll dig in.
I suggest you try playing Brazil. They are a good size nation, you can join any faction, you have no enemies on your border to worry about. If you go axis, do the same thing as above...build your nation up and buy PLs. Make coastal forts in each of your ports (go up to 10 if you can) and place 2 divisions in each. If you join the Axis, go to war with the Allies and try and grab the territory up north (UK/French/Dutch) as thats likely where an invasion will come from. The French territory will turn over to Vichy France, which may cause you a problem (leaves an opening for the allies). Do not invade any South American nation until the USA is fully embroiled with Japan or they will hit you with the wrath of god.
You can get Lendlease from Germany, Japan and Italy (although Italy wont be able to reach you until they take the Suez or Gibralter). which will give you a crapload of IC. If you want to have some fun...buy about 4-6 landingcraft PLs from Japan, take those along with your entire navy and about 6 infantry divisions and ship them to Sardinia (Italian island north of Tunisia, west of Sicily). When Germany invades Poland, load the troops up and send them to the Atlantic (just past Gibralter). DOW the Allies and amphib Gibralter (leave 3-4 divisions there). This would allow you to begin getting Lendlease (from Italy) right from the start of the war, and it also will hurt the UK by closing off half the med.
When your ready to make an enemy of the USA (all your ports have forts and divisions in them), launch an amphib from Northern Brazil (the UK conquered area is best) into Colombia. Make sure you have at least 10-12 divisions (some German armor would be nice) so all in all you should be 10-15 landingcraft from Japan. Take Colombia and head straight for Panama and close the canal. This will really hurt the USA. Fortify the hell out of it, coastal and land forts, airbases etc... the USA will send wave after wave to their doom trying to take it back.
The trouble comes when nations that border you go Ally, allowing for troops to enter there. Use Panama as a choke point. Fortify it well, then you can start taking other South American territory. take the ones up north first as they will need to be fortified the most. Eventually the Allies wont be able to reach you buy sea, only certain spots.
Go get them!
Your welcome. Enjoy!