Problems snapping and extruding

Staying focused on your problem.  I found nothing wrong with your sketch to prevent it from creating an extruded feature.

The first thing I noticed is that you were trying to do the extrude as a contour (the shaded 5 sided polygon with a hole in it next to Sketch 1 indicates the feature was made using contours .

I suppose this was because some of the sketch problems you described in your original post (SolidWorks defaults to using contours when it does not find a closed sketch) caused SolidWorks to try and make the feature using contours.

The reason, after you fixed your sketch, it did not extrude properly is because the contour was lost.

To get the extrude to work

• Edit the Boss Extrude feature
• Click in the Select Contours box (turns blue)
• In the graphics area, select inside your sketch (inside turns what looks to me pink).
• Click the green check to close the edit

Or if you do not want to use contours; delete the extrude feature and add a new one.

How you model is a matter of personal preference.  Certainly keeping things simple when you are first learning is good advice as are the rest of the points J Mather makes.  The only one I have issue with is adding fillets as separate features (my opinion).  On simple sketches or models that have just one extrude, I would recommend putting them in the sketch.  One more complicated models, I would recommend putting the fillets in as features.  As I first stated, how you model is a personal preference.  As you use it more you will find when it is better to model one way over another.  How complicated you make you sketches depends on who will have to use them later.  If it is you then no problem.  If it is other users then take care you do not make your sketches so they are difficult to edit.  And always fully define a sketch (lines and arcs turn black).