U Srinivas - Tiruvadi Saranam (2/3)

Wonderful music!

looks pretty much like a 6 string electric guitar with a mandolin neck, right?

yes a five-string solid body with highly resonant exotic wood (my guess)

Pretty much like heavyatheart mentioned. The head is from a guitar, but he uses 5 strings tuned CGCGC. In Indian music, since notes are defined as a "shape" rather than a pitch, the only real definitives are the tonic and the fifth. Similarly, the violinist also tunes his strings CGCG. The drummer also tunes both sides to C (the bass side one octave lower). More accurately, I should say tonic-fifth-etc. since the tonic can be different when accompanying a singer who sings in some other key.

Since the instrument is tuned in 5ths, and played in one key, he could actually have a mandolin built that is in a natural tuning instead of equal temperament.

What kind of distortion does he use with his mandolin? What's a 5-stringed mando- called?

only echo and delay. nothing more.

where is the drone in the background coming from

The drone sound is from the tambura. The woman in the background is running her fingers across the strings repeatedly to generate the sound. Although those things can be substituted using electronic devices these days, a lot of purists prefer the "warmth" of the genuine article.
It's the standard background soundscape used in movies when representing "India." Westerners often mistake it for a sitar because they're unaware that there are stringed instruments in India other than the sitar.

for him it is like child's play. Interesting to see how he uses fingers to pick on the top strings.