Don - KM4UDX
Dean and Skip speak wise truth. Do what they suggest, and your path will be fruitful.
Every builder I know who rushed into adding the AGC board, or adding the spur reduction mod, or added a fancy external mic, or changed the relays, or or or had a MUCH harder time of it, and typically they give up in frustration, and uBITX never got happy on the air.
So, build it as suggested in a pizza box, or plastic box, or anything that is easy. It is much more important to leave the physical rig exactly as designed, and then move on to loading the CEC software so you gain rig control for WSJTX or FLDGI, or HRD, or whatever software you use which controls the rig.
So, in short,
1) build it as is, tweak BFO as needed,
2) load CEC software including memory manager
3) get your digital mode or logging application of choice to exercise uBITX rig control
4) use the radio (lots)
5) then, and only then, mod based on what needs YOU experienced in step 4 above.