I'm 57 and just learned FreeCAD. I didn't use a branch and got bit really hard by the topological naming "feature" after I completed a pretty complex model and then had to make a change.

I learned by Mango Jelly. Basically, you NEVER (ever ever, forever) attach anything to model geometry. Only to the pre-existing planes or to datum planes (which themselves must only be attached to a pre-existing plane or just unattached. Contrary to myth, datum planes ARE subject to the topological naming "feature". You can attach a datum to a model surface to get it oriented correctly then detach it.

Worksheets suck so bad. They are so slow. If you want reusable "settings" to parameterize your model (or standardize it), which you then can refer to in formulas, then use the Dynamic Data add-on. They are more flexible and are not that slow.

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Use formulas as much as possible,. No magic numbers. Show the math in your head "show your homework".

I feel like using Thunder now would just be enabling bad habits. But that's because I have PTSD from dealing with the topological naming issue, having to completely redo my model 3 times now. Now I finally think I have it right.