I am currently doing a major overhaul on my K40. It may be excessive for some however everything can be moved to a larger bed.
I will be using the UB40OB expansion. I did consider another one however the UB has the advantage of not needing cross members, and the other one that did you could not just drop the new frame in to the K40 Case. Also you are using the case as part of the overall framework.
Upgraded the tube to a 60W 55mm x 1250mm tube. Will be using 100mm acrylic tubing to protect the overhang outside of the K40 case. Have new power supply to handle that. Will also set the tube back a little so I can have a beam splitter and laser pointer installed before first mirror.
Been looking at a simple DIY scissor Lab Jack for the bed height. The main screw can be run cross the base of the K40 case so to give a low profile. This also means that there will be very little supports going across the work area so I can lift out the cutting bed and drop in my rotation mechanism
Processor. Will be using a MKS SBase with a 100mhz processor. GRBL. I have also decided not to keep the MXL belt and gears, but go to the more standard GT2. I already have an CNC machine using the same so working out the new values will be easy.
As for ventilation - I have run a 90mm storm warter pipe around my shop. This has an extractor fan at the end and T-pieces ever meter. Since I have 2 x 3D printer, CNC, and Laser it is just a case of un-stoppering a T piece and plugging the unit to be ventilated in.
Cooling for laser will be a home made chiller using 2 x 15A peltier devices. Each Peltier device has 2 fans, and will be software monitored.
Wish me luck