Basically what I said. If I convert and become a Muslim, am I required to grow/maintain a beard?
While it is NOT a part of the core principles of Islam that you must maintain beard to be or stay Muslim, it is highly recommended part of the attire of a Muslim male.
To some school of jurisdiction, (e.g. Hanafi), it is obligatory, but not part of the basic believes as I mentioned earlier. Hence, dropping it intentionally is considered a sin. But, still Muslim.
The above short explanation is applicable in general, however please also keep in mind that Islam also don't burden someone beyond his/her abilities or context.
ALLAH knows the best. I just tried to give an idea of the concept.
Growing beard is a Sunnah. You will be rewarded if you do it, but it is not a sin if you don't do it.
No. You would still be considered as a Muslim. Growing beards is highly encouraged in Islam and considered as a Sunnah. But not growing one won't make you a non-Muslim.
If I convert, must I have a beard?
Of note, albeit having beard from Islamic view of point --at least based on Shia Islam-- is regarded as a necessary/wajib (mandatory) act, but it doesn't mean that if you shave your beard (and if you don't keep your beard in its at least Islamic size) you are not a Muslim anymore!
Hence, despite shaving your beard, you'll be still a Muslim --if you have converted to Islam or you have born as a Muslim-- but pay heed that it can be regarded as a kind of sin or disobeying if you don't obey his order or ...