The Turks would not just be fighting the Kurds though.
They will also have to face the Syrian army because Assad has vowed to recover every inch of Syrian land. The Kurds have asked for his support and the Syrian military have deployed to Manjib.
I was reading an article the other day from a well known source, I tried to find it to include a link but I couldn't and gave up.
The analyst basically wrote that Erdogan has asked the US not to withdraw to help him in Syria to fight ISIL - which was basically a cover for him to fight the Kurds. More or less everyone knows this and his motives cant be trusted. The article was explaining how wrong it would be of the US to remain in Syria to help him at all.
Furthermore the analyst said despite Turkish military numbers and assets, they are not very good at fighting against scattered militia. The Turkish army is good at going up against large army's, primarily to suppress them. They are also disorganized because they rely on others to provide them with the intelligence.
The Turks can barely manage do anything by themselves, unless their opponent is more or less defenseless.