Just about all the downtown hotels here in Indy are decent, but you may find them already booked for Final Four Weekend...The Marriott you mentioned is also decent and is close to downtown.
As for the nightlife, Downtown Indy will be rockin' that weekend!!!...We know how to put on a party...we do it every year in May for 400,00 of my closest friends!!!...
The main concern is the weather that time of year...It seems that just about every Final Four we have hosted here in the last couple of decades, there has been severe weather at least once over the course of the weekend. And I'm talking severe thunderstorms and even tornadoes...
Have fun while your're here, spend lots of money, then get the hell out that Tuesday!!!...
(j/k)