Fog on windshield

The heater core could be leaking-sounds like a freeze plug the way you described it-

That certainly sounds like a heater core. They have to leak pretty bad before they leak onto floor. Remember that the heater box can catch some fluid and it can leak gaseous anti-freeze as steam. That is what you see on the windshield and that is the smell you are getting a good whif of. You could also have a leak at one of the heater foses right at the firewal. That might explain the leak you see on the ground and the smell. However the core is more likely bad as the vents are pumping the steam out, but keep both in mind.
There is not anything that can leak anti-freeze between tranny and block. There are some engines with freeze plugs but I have never seen any in the mating area of the tranny. Anti-freeze leaks can be deceiving as they can drip from a higher place, follow a path by surface tension which will make the fluid, "cling" to surfaces and make the puddle show up somewhere that is not near the actual leak. You have to trace it from the ground up. Remember to check anything that is in the path where the drip came from as you might trace a hose that goes to the firewall several inches from the puddle as it has clung to the hose and travelled down it to the lowest point and then dropped off.
So, I think that you probably have one leak and it is associated with the heater core of the core hoses that go into the firewall and the leak would have to be right at the firewall for steam to get sucked into the heater tract. I guess if it is coming through the A/C as well that does make it harder. Sometimes vent doors don't shur or seal all the way after time or the heater core valve does not close all the way and the air still passes by the core but fluid is supossed to have stopped flowing. A bad valve can make your A/C inefficient.

If it is the heater core you can do a bypass by taking one of the heater core hoses off at the firewall and disconnect the other hose at the block. Then take the hose from the heater core and route it to the connection at the block for the other hose. This should really be done with the hose without the heater core flow valve on it as it might affect the bypass. When you do this you are running the coolant that would be going into and out of the heater core in and out of the block where the 2 hoses connect. So one hose stays connected at the block but disconnected at firewall. The other hose disconnects at the block but stays connected to the firewall, this one does not matter as this hose will no longer have fluid in it.
Then the hose from the connection at the block goes back into the hose you disonnected from the block looping the fluid in the hose and keeping it from going into the heater core. If that does not help, you probably do have a freeze plug that is blown out enough to leak and it is near the tranny block or it could be at the back of the block in the mating area, I just have not seen a block like that but I am sure some manufacturers put freeze plugs there. So, you can look around the block halfway in between the oil pan and head you will see dish shaped plugs about an inch or two in diameter that are press fit or actually beaten into the block with a special tool. Look for ones that look pushed out or past the edge of the block face or show signs of leakage. To check the tranny/block area, pull the tranny inspection cover and see if there is an accumulation of anti-freeze. You probably won't be able to see the plug but you might. You can bang in the plugs that have been pushed out with a rubber mallet. If you damage them or drive them too far you will make the situation so bad you won't be able to drive the car. You can buy cooling system leak stop or head gasket leak fix that sometimes works depending on the size of the leak. This will pollute your cooling system and if you ever get it fixed you will need to really flush it out. Do not buy a PERMANANT head gasket fix as they can cause other problems. Hopefully the sealant will clog the hole and you will be on your way. You can first try a raw egg directly into the radiator as it will act like radiator leak fix and seal small leaks for a while. Keep a carton with you. They won't pollute your system as bad either.
The real issue is that the coolant circuit froze or is corroded bad enough that the cre is rotten or a reeze plug has been puched out as they are made to expand out when coolant circuit freezes. When either happens you can expect other problems to show up like a bad radiator or a head gasket leak or the worst is a crack in the block which will occur at the lowest point in the sytem becasue water is heavier than anti-freeze. Anti-freeze will only last a few years or so many miles depending on what you use. Then it loses its ability to hold water and keep it from freezing. The water falls out of the Anti-freeze/water blend or freezes the fluid in place.
You have the options to get you by but you will be looking at a repair that needs to be thorogh in order to avoid other issues in the futire. Teh best thing to make sure you do in the end is a coolant system pressure test and try to get a, "leakdown" test as this will tell you how long the system can hold pressure. If it can't hold the pressure even if it can make it it still has a small leak somewhere.

You are very welcome. I have been in the same situation and the, "Heater core bypass surgery" will get you by, just no heat and your A/C won't stink. Unless there is another issue. The vent steam and smell sound like heater core and the leak sounds like freeze plug. The next time you get a chance after doing the bypass, grab the upper radiator hose right after turning off car to see if it feels like it has pressure in it. That may be a good sign that the heater core was it or that any other leaks are small as they can hold pressure in the system. Pressure is necassary for it to work properly.
Let me know how it goes and if you have any questions, I will get back to your reply ASAP. I work pretty regulary all day and night when I can but I at least catch the 5PM EST til 10PM EST after dinner rush.
Top off the fluid as well after the bypass. You can use distilled water since your anti freeze is pretty much water anyway.