Just realized that I confused "Antalya" with "Ankara". ARGGH!!!! There are too many places names that begin and end with the letter "a" in this world!
Anyhow, until you near Antalya the scenery is quite bleak. Bus and airplane are your only real choices for transport. The journey takes about 11-12 hours by bus (costing about 30 AUD) and it's particularly good as an overnight journey as with an early evening departure you'll have sunlight for the portion with good scenery. There are seasonal direct flights but in January your only flight choices will be via Istanbul.
Absolutely no need to book your hotels for the road trip portion in advance. Some of the coastal resort hotels will be closed for the season but you find some great deals at those which are open.
Pamukkale is a wonderful and unique place but it is well inland and fairly high in elevation so winter weather might be a problem. The backtracking route there (from and returning to near Izmir) is probably the best way to avoid any problem with the weather. I was stuck just south of Denizli on the most likely highway you would take were you to go there directly from the southern coast.
I've spent time in Turkey during all four seasons now and truly love it anytime of year. Unfortunately however you don't have a great chance of truly nice weather in January. The southern and western coasts have a Mediterranean climate with warm dry summers and cool, wet winters. Overcast skies are common and such prevents the sea from taking on its amazing blue color. Cappadocia will probably be freezing between evening and morning but most days will get above the freezing mark for at least few hours. Despite being quite far north (it is the same latitude as Chicago, Illinois) Istanbul is blessed with moderate temperatures. We were just there a month ago and saw old trees considered "tropical" blooming.
I've done little international traveling during the winter but I have done quite a bit during the late fall and some in spring. While I still suggest Turkey if you want warmer weather you might consider Egypt and perhaps Jordan. We were in Egypt during April and there are some incredible bargains as tourism is still VERY low. Jordan is an amazing place--we visited in November to perfect weather--but January is the most likely time to find rain and crazy, multi-day sand storms.