All you need to install your e-Sword HD module at no additional cost is to enter your Email address and "Product Key" you received when you purchased the module for use with e-Sword. If you do not have that information, just tap on the "Recover Product Key" button on the popover that prompts for this information.
No. E-Sword HD is an "offline" app. An Internet connection is only needed for downloading the app itself, and any additional modules you wish to install.
No. Only iPad models running at least iOS 12.0 (which is available for all generations of iPads built from October 2013, e.g. iPad Air.)
There is a lot to it, but hopefully we can make it easy for you. The following steps should assist you in this endeavor:
STEP #1 — e-Sword. You need to have a PC with e-Sword 11.0 installed on it. You can download that from here: https://www.e-sword.net/downloads.html
STEP #2 — Content. There are thousands of user-made modules already available for e-Sword which can easily be converted for e-Sword HD. Join the e-Sword User Group where you can find what you are looking for, or if it doesn't already exist there are also tools by which you can create them! The e-Sword User Group is here: http://www.biblesupport.com/
STEP #3 — Convert. After you have downloaded the e-Sword module(s) you wish to convert for use in e-Sword HD you will need to run them through the e-Sword PC to iOS User Module Conversion Utility. You can download that from here: https://www.e-sword.net/extras.html
STEP #4 — Transfer. The final step is to move the new module(s) onto your iPad. You will need to have iTunes installed on your PC to accomplish this. Detailed instructions on moving files onto your iPad using File Sharing are here: https://support.apple.com/kb/HT4094
STEP #5 — Restart. To load the new module(s) you will need to restart e-Sword HD if it is already running. During the startup process e-Sword HD will pull the module(s) into its sandbox and load them. If there are any problems with a module it will be deleted!
WARNING!!! When you connect to the iPad with File Sharing you will see a bunch of files. Leave these alone as these are your user files! You can certainly back them up if you want, but do not delete them! Also, do not copy any files that were not created with the conversion utility as they will be ignored by the app and this directory is backed up to the iCloud so you could run out of space there!