Question about Bar Mitzvah Minhagim

Can anyone share some info on Bar Mitzvah minhagim according Minhag Ashkenaz/Minhag Ostreich?
The info in Shorshei Minhag Ashkenaz seems to deal with more ancient customs.
It says that a bochur does not receive his first aliyah on a weekday but rather waits until the first Shabbos after the Hebrew Birthday.
But is the actual Hebrew Birthdsy marked in any way?
Is it the minhag to have a Bo Bayom Seudah on that day?
Is it the minhag to serve pastries in shul on the first day putting on tefilin as is seen is some congregations?
Any info would be appreciated.
Thank you!
-David

What about a kiddush in shul the first Shabbos after the Hebrew birthday?
If the bo bayom is on Monday or Thursday is there still no Aliyah until Shabbos?

According to Minhag Ashkenaz is there any special celebration done on a bachor's first day putting on teflin?
It seems like in many Eastern European shuls people bring donuts and/or herring and schnapps on this day. Is this according to Minhag Ashkenaz?
At many son's school it seems like a vast majority bring donuts and/or danish on the first day putting on tefilin.

According to Minhag Ashkenaz, is Shir Hamalos recited before bentching after a bar mitzvah seudah that falls on the Hebrew Birthday?

How far in advance of a Bar Mitzvah should a boy start to put on Tefillin? One Month? Three Months?

Thanks.