To get to Izmir, the easiest way is to catch a plane.
The Turkish roads are not in good condition and journey times from Istanbul are very long.
Izmir is a seaside resort popular among tourists. So don't expect to be in a city which is only full of locals.
Regarding accommodation, you don't need to be constricted by the establishment's number of stars. Indeed, the norms in Turkey aren't the same as in France. You can quickly find yourself in a 8-star hotel which would be considered two in France.
Not to miss: the Kemeralti bazaar in Izmir. A place full of colour and exotic smells. There you will find spices and jewellery but also clothes and other decorative objects.
Next, the nicest beaches are in Çeşme, approximately 80km from Izmir. You can hire deckchairs and parasols on the beaches: it's all at your disposal! However, one piece of advice: take as few personal belongings as possible with you. Indeed, thefts on beaches are common, and spending your holiday with the police station and the French consulate is not fun!