"missing" numbers are not important, important are only top blocks numbers, this is how is connections order working:
blue is order, and next colors are blocks runned in each blue order:
0_1484164228379_upload-21b5ef27-0a10-4172-8bb2-2693e263b502
somewhere in help you can find next explanation for this ...
and the blocks what you mean as "hidden" are not hidden, it are normal blocks in fxdreema, but they are only renamed (right click - rename) (I left original name in begin of this block) .... only "Custom MQL4 block" is little special, because here you can type own "math" or some functions, working with variables in text, etc. ...