That’s an ambitious plan and there’s no reason why you shouldn’t do it, but I have some perspectives to add: you can drive all over Tamil Nadu, yes, but cannot stay and experience much of it in the time you have in mind; also, of course there are hundreds of villages in TN, but they aren’t really equipped to welcome tourist-travellers, and qualitatively recommendable 4/5-star hotels are thin on the ground except in the state’s urban agglomerations, which is true of most of India. I am also not able to arrive at your particular interests based on your desire to visit Kanyakumari (the coastal temple town high on tourist itineraries), Kolli Malai (untouched hill range in the Namakkal district) and Theni (a trading town on the border with Kerala). So, I’m leaving you with a possible route featuring adequate night halts, skipping over obvious suspects like Pondicherry, Tiruchi, Coimbatore and Kodaikanal, which you can easily weave in, and keeping most distances at or below five hours of journey time, depending on the roads. I have put in suitable star accommodation where I could find it. Here goes:

Chennai-Tiruvannamalai (Sparsa Resort on Athiyanthal Village, Chengam Road; they don’t have a website)-Thanjavur (www.duneecogroup.com/our-hotels/tanjore-hi)-Thirupugalur (www.mangalaheritagehome.in)-the villages and towns of Chettinad (stay at www.sarathavilas.com in Kothamangalam or www.thebangala.com in Karaikudi or www.cghearth.com/visalam in Kanadukathan or www.chidambaravilas.com near Pudukkottai)-Rameswaram/Dhanushkodi-Thoothukudi-Kanyakumari-Tirunelveli-Dindigul (www.rajakkadestate.com)-Theni-Pollachi (www.shenbagavilaasam.in)-Kolli Malai-Dharapuram/Bhavani/Sathyamangalam-Hogenakkal-Arcot/Yelagiri/Vellore (www.grthotels.com/vellore)-Chennai.

Ideally, you should give over at least 3-4 days to explore the culturally rich rural vistas of the Thanjavur delta, connected by excellent roads and intersected by the Cauvery and her tributaries (apart from well-known towns like Tiruvaiyaru, Tiruvarur, Kumbakonam, Swamimalai and Nagapattinam, you could swing by tens of remote villages like Melattur, Thirukarukavur, Thirumeeyachur and Mannargudi). Enjoy the flexibility of driving alone and explore at will. Your trip should yield quite a few happy surprises.