Rack & panniers, full mudguards, go full commuter bike. 
No, to start with whatever you have is Good Enough.
If you find yourself committing to months of commuting then you’ll soon realise a backpack (anything you carry) is literally a pain. Removable mudguards also soon become a hassle. I’ve commutes lots of ways, after several years I got me this Italian steel beauty, although I’m basically a fair weather commuter now.
I’m even wearing flats and trainers (no power meter!)
I was surprised last summer with how effective a merino polo is, and working without changing or showering.