I’m designing a built-in home office using IKEA METOD (Sektion) modules. The total width is 300cm, squeezed between a curtain (left) and a radiator (right). It needs to accommodate two people working side-by-side. In pictures the Wall, the project and a render. 

The Layout:

Two 30cm side columns made of stacked METOD units (Total height ~270cm).

A 240cm desk made from an IKEA countertop (looking at Oak finish).

4x 60x80cm METOD wall cabinets at the top.

A 240cm wide, 37cm deep floating shelf in between.

I’m looking for some expert "hacker" advice on a few points:

The Base/Plinth: I need to raise the side columns by about 10cm. What’s the best way to build a solid base? Does IKEA have a specific white cover/trim that works well to hide a DIY wooden base and matches the METOD white?

Desk Support (240cm span): Since the desk is 240cm wide with no cabinets underneath in the middle, I’m worried about sagging. What’s the best "invisible" support? Steel stiffener bars, a hidden cleat on the back wall, or should I just give in and put a single ADILS leg in the center-back?

Cable Management: Should I drill grommet holes or leave a 3cm gap between the desk and the wall? I’m leaning towards the gap to avoid damaging the countertop, but would love to hear pros/cons.

Aesthetics (The "Tyssedal" look): I have PAX Tyssedal wardrobes nearby. Since Tyssedal isn’t available for METOD, which door style is the closest match? I’m looking at AXSTAD (white shaker) or ENKÖPING. Any thoughts on which looks more like Tyssedal?

The Giant Floating Shelf: I want the 240x37cm shelf to have completely invisible supports (floating). Given the 240cm span and 37cm depth, are heavy-duty blind shelf supports enough, or will I need to anchor it to the side cabinets too?

General Improvements: Any suggestions on the overall design? I have a radiator on the right, so I’m leaving some breathing room there.

Thanks in advance for any tips, tricks, or "I've done this before" warnings!

Planning a 300cm METOD Home Office for two. Need advice on a 240cm span desk and floating shelf!