Can I start a sentence with a number? If so, do have to write the number out, or can I use the numeral (if it is over ten)?
You can start a sentence with a number.
I don't see what difference it makes if it is less or more than ten. Also you don't have to write it out. Two examples would be the following. 10 Rillington Place is a very powerful film about the Christie killings. 2,000 LIght Years From Home is a brilliantly innovative track by The Rolling Stones from Their Satanic Majesties Request.