Im new, am a 3D designer. Need a New cnc machine and need advice and guidance

[JAZZCNC]

My one concern is the accuracy in welding...if i take the parts to a welding shop will they know how precise this had to be? Dont want them to weld it up and realise its off by a few mm

Don't waste your money because they won't be able to stop distortion only lessen it and in any case you will still need to either use shims or Epoxy method.
Only thing you want to pay special attention to is Twist. If the base frame is twisted then the rails are not on the same plane, Epoxy method is good for sorting this but if you pay carefull attention when welding up then it's possible to get away with just light shimming of the rails. . . BUT with your design the Epoxy method will be much easier and more accurate than your capabiltys to measure rails are on same plane.!

Squareness of base frame isn't critical either square to 1 or 2mm is fine, obviously less is preferable. The important area is the gantry is square to the rails.
The base the cutting bed sits on needs to be resonably flat but again it's not critical as you'll surface the bed before using and this will bring it flat parallel plane.

Like Neil says you really need to go reading some of the build threads more closely and pick up the tips and you'll see whats needed and where your design Lacks or CAN be improved.