It is no problem to build a DIY machine to meet those needs. 2" square box is a fair start for frame but note that the 1/8" wall is a bit thin where you need to mount the rails. Usually you would add a 5-6 mm strip of metal on the inside to reinforce the mounting point and get a decent length of thread engagement. Also if the gantry is made from this it should really be multiple sections joined together (i.e. single 2" box is not large enough to create the beam).

That kit of linear motion parts you linked to is a good all round set of sizes for X, Y and Z, with 20mm rails etc, but the pitch of the ballscrews is only 5 mm. I have that pitch and it is ~OK, but starting again for wood working the advice is go for 10 mm. You could email them and see if they have 1610 instead of 1605 ballscrews. This gives you the speed you need for wood. You might think that you can add a pulley ratio and drive the ballscrews twice as fast but then you are in danger of the ballscrews whipping (the long ones anyway) due to the higher rotation speed.

For machine designs there is the fixed gantry style and moving table (which is very rigid but requires lots of space) and there is the moving gantry type which gives a much large working space for a given footprint.

The moving gantry type is generally use for wood working. This can be split a bit more into frame gantry where the gantry has sides dropping down to the bed:
Click image for larger version.  Name: IMAG1088.jpg  Views: 408  Size: 371.7 KB  ID: 22870
(c) Dean/Jazz

and beam gantry, where the bed is raised up to give more stiffness but can limit access for sheet feeding onto the machine:
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(c) Clive

On this forum we would usually recommend the beam gantry because of it's versatility (extra stiffness helps for aluminium cutting), but strictly for what you want to do the frame gantry would be fine.

If you post some sketches, even hand drawn and scanned in if F360 skills are not ready yet, then you will get more detailed advice from this forum.

Finally, here is a link to the finished machines gallery to get you going:
http://www.mycncuk.com/threads/10066...s-picture-menu