Unfortunately, that box set was released for Late War back in Version 3. Version 4 was introduced a few years back with Mid-War, and has only just started bringing Late War into the fold, as a consequence there are currently no rules for the M26 Pershing, and both the rulebook and Bridge at Remagen army book are useless unless you find someone who still plays V3.
The Shermans and Armoured Rifles can be used, however you will need other kits to make a complete force for V4
The current Late War offerings for Americans are covered by the Fortress Europe book and the D-Day Americans book, but it's the D-Day book that will give you the ability to use the 76mm Shermans your starter box came with.
Fortress Europe was a book designed solely to allow people with V4 Mid-War armies to use them in Late War until nations recieved their proper LW
updates, and while it can still be used in conjunction with proper LW
books, it lacks some options that didn't appear until the D-Day period.
As for list building, Battlefront have their own list builder here: https://forces.flamesofwar.com/
It costs a dollar or so per company you buy access to (with a small discount for buying access to multiple at once), but functions decently well as a general list builder. One thing to watch for, though, is that when buying the companies you want, double-check their item codes - the catalogue is difficult to navigate since it mixes LW
, and lots of the companies have identical names (such as Tiger Tank Company, a list which appears in several different books under the same name).
You don't have to use Forces, especially if you've already paid for the book, but it's cheap enough and fairly handy for spitballing list ideas.
So basically, what you'll need to play Late War is:
- Latest Version 4 Rulebook
- D-Day American Book
After that, you can look through the lists on offer to see what needs adding to your force in terms of models.
The Organisation Charts themselves can be a bit daunting, but once you get your head around them they're fine. Give the Version 4 book/lists a glance over and if you've still got questions then lay them here.