They treat foreign pilots DECs much the same as the Turkish in terms of roster etc, in terms of your value, you are a resource, simple as that. You will not be enjoying the close relationship with training and management as the nationals.
Admin takes a long time and can be frustrating, work permits, resident permits etc, often confusion and delays, this is normal in Turkey.
Training will take longer than planned and during this period do not expect to be able to leave Turkey. Use this period to get accommodation etc planned, in Turkey tenant pays all the agent fees etc.
Some guys live on the Asian side some the European side, we are told this year most flights will be out of IST, the SAW flights will be planned mainly using a partner airline , so probably only about 10% from SAW for THY guys.
Living in Istanbul is good, costs vary considerably by area, about 4000TL will cover normal living costs .Cars are expensive ( about 2x UK price), fuel is expensive, driving is a nightmare. Public transport is good but delays on the bridges can cause problems if travelling from Asian to Europe side etc. Sea ferries are reliable but stop late at night.
Company provides travel allowance, just covers costs if you live on European side, falls short if you live on Asian side, allow about 2 hrs to be safe to get to work from Asian side if you use public transport.
Roster is fixed, mainly 5/2 6/1 with min 7 days off a month , you can request 3 days in a row, but it may not be given every month, expect to fly up to 100 hrs a month and duties are long, mix of international and domestic.
Lots of national holidays and during this period don't expect to get time off as priority is given to locals.
Pay is reasonable, 5% tax is payable, healthcare is insurance based, covers about 80% of treatment costs.
With Turkey not being EASA state, allow time for licence issues and medical checks.
THY is populated with ex military and expect some CRM issues and authority issues, but on the whole things are moving in the right direction. Some more foreign FOs arriving but normally two foreigners are not planned together.