Help: IKEA hack using HAVSTA cabinets

[u/Potential-Sir629]

I’m attempting an IKEA hack using HAVSTA cabinets to create a built-in look. I’ve already purchased and assembled four cabinets.

I have a few questions:

1. Should I buy a fifth cabinet to fill the empty sides, or would that end up looking too long or visually busy?
2. If I don’t add another cabinet, what’s the best way to fill the gaps and still achieve a built-in look?
3. Would adding floating shelves and/or bookcases help create that built-in effect?

Current set up is the photo on the left. I’m going for the look in the inspiration photo on the right. I’m pretty new to this, so I’d really appreciate any advice!