Advice on z-axis modifications for Openbuilds Ox

Hello! First time posting here. I would appreciate some advice, please. I am currently in the process of building an Ox (750mm x 500mm), with 4x Nema 23. I only have the mechanical kits at the moment and am planning to get a Duet3D as the controller. The Ox will be used mostly for laser cutting using a diode laser, as well as relatively light CNC work on wood (max 20mm or so thickness, but using oak). I would very much like to make some modifications later, to incorporate 3D printing. I realise the arguments of having a separate machine for 3D printing, but really do not have the luxury of space to accommodate another machine. As far as 3D prinitng is concerned, it is only likely to be a a small part of use, but perhaps more as the kids getting into it.

I would very much like a 3D build volume of 500 x 300 x 300. No issues using the Ox for the 500 x 300 XY but obviously the depth is limited (seems to be an absolute maximum of 70mm travel on the current 200mm z-axis. There are loads of different modifications shown in the forums, but does not seem specifically for modifications for 3D printing.

As I see it, there are two major limitations of the Ox in this regard:
1. The X-gantry clearance is an absolute maximum of 175mm (150mm with the Z-axis in place) and no base in place
2. The z-axis travel is a maximum of 70mm

For the first problem, I think my options are to either raise the X-gantry or to drop the base by using more extrusions and lifting up the the whole Ox. I think the latter might be preferable? I did get a second spoiler board support bearing this in mind.

The second problem is the one that I cannot find a collective opinion on. I can think of 3 options...
1. Replace the current 200mm z-axis with a 450/500mm extrusion and appropriate lead screw which should give me 320/370mm maximum travel ?
2. Replace the current 200mm z-axis with a 500mm C-beam ? I presume this would mean that the spindle / laser would move rather than the extrusion, and I would need to mount the 3D extruder on a further extrusion, which is then in turn mounted on to the C-beam?
3. Build a z-axis platform at the base with 2x lead screws with 2x Nema 17 motors? The 200mm Z-azis will be as it is. The spoiler board will go on as per normal on its supports when using the Ox as a CNC / laser cutter, but remove the spoiler board and use the z-axis platform for 3D printing, with the current Z-axis raised to its maximum height. This would be the most expensive and complicated option but perhaps the best?

I would very much value what people think... Thank you