Hooo boy, that replay was almost too hard to watch.
You didn't really pose any answerable questions in your post, so I'll outline your mistakes and how to improve.
1. Mortar. Simple counter to intense blobs and even Leigs, but you need to support and defend it.
2. Sniper play. You need to be more aggressive, your sniper wasn't doing anything for most of his life.
3. AEC play, you also need to be more aggressive, you really could've established a foothold with your aec and sniper, but you were very passive with both.
4. Capping order, with your first IS, you went forward, and then backwards to cap, which left your opponent to take what you had, as you weren't covering it with anything.
5. Wrong commander choice, you only used the halftrack? You really could've won if you went with artillery cover or Vanguard operations, go with a commander which you will make the most use of.
6. Firefly use, you need to rest them behind all your units and act it as a support weapon, not second line with your infantry, as they get shrecked. And your really didn't need to get three...
7. Crocodile. I was waiting the entire game for the Croc, as he wouldn't have had any effective counters until his 35 min jagdpanzer. Croc destroys infantry and tanks, as well as being a sponge. Attack, repair. Rinse and repeat.
8. Armour micro, you lost all your tanks because they weren't supported by infantry or they were by themselves on the frontlines, combined arms is the key during the mid and late stage.
I missed some stuff, but those were the most pressing issues.