I am aware that grid based movement is possible in Unity using JS or C# & a little help from A* algorithms
However, would it also be possible to control the player with an in-game / on-screen keypad?
Let’s say: player 1 needs to move 4 places forward, turn 90deg left, forward 2, 90deg right, forward 8.
Input this data into the key pad and press “Go” player moves smoothly along the set path!
Is this possible, if so if I can be pointed in the right direction would seriously help me out!
You can use a list to store a sequence of movements, then execute them in order once the player has finished the sequence
If I understand what you mean, you want to instruct your players though text. You first need a language to read from. E.g.
player1 step 2
player1 rotate 90
player2 step 5
....
You’ll need to parse that to actual game logic. Parsing that is up to you 
To ease the process, I recommend you to use coroutines. Coroutines will make your behaviors wait for other actions to be performed. Probably, in the example above, you want them to be sequential and synchronous (i.e. rotate 90 starts when step 2 has finished). Read more here.