I could download and install the BTG wallet and then simply import the keys from Armory? 
Of course... you have access to your private keys within Armory and the forks have wallets that allow you to import keys.Easy solution:
- Export keys from Armory
- Import keys into "ForkCoin" compatible wallet
-
- Profit
BCH and BTG both have "Electrum Forks" (Electron Cash and ElectrumG respectively) which make importing your keys and moving your fork coins ridiculously quick and easy... you don't need to download any blockchains and assuming you take the proper precautions (ie. moving coins from keys before importing into another wallet, in descending order of value) you don't really need to worry about the security of your coins.
Or you can continue attempting to connect Armory to "forked" blockchains which it has likely not been tested against and/or hope that goatpig finds time to create "signers" for various forks...
I don't have that many transactions. I guess I'll use the configuration in your post https://bitcointalk.org/index.php?topic=3274219.0
For each transaction I'll just copy the data to a thumb drive and label them transactions 1, 2, 3 etc. Then take them to the new BTG electrum wallet and import them. The offline wallet will be more difficult but it should be ok.