No problem guys. I wasn't really doing much either.
But I had a bit time recently and did some progress. I got most of the install reduced using modules or combining codes into already existing add-on files.
Right now it requires 2 code additions/changes inside 2 files. And it only works with the FROZEN version (PHP 7.0.21). EDGE and GOLD are not supported at the moment.
I also got the catalog side layout done. I can create a custom product now and add it to the cart. I must say the add-on is very difficult coded. A lot javascript and onclick functions involved but it does seem to work.
I didn't had time to test it further than that. Didn't go into the checkout and I don't know if it reduces the stock of the added items.
The only real bug thus far is the image dropdown selection after a custom product has been deleted. You'll know what I mean once you try it out.
So here is the package for those who are interested to have a look at it. (Please do not install and use this in a live store! You have been warned.)
Custom-Product-Builder-for-BS-Tsimi.zip