Hi. At Tirumala, after Darshan, u can visit "Shila Thoranam" (Natural rock Arch. belief is that Lord Balaji entered through this Arch), Kapila Theertham (holy pond), "paapa vinaashanam" (used to be a sacred natural one but currently an artificial water fall), and there are at least 10 temples/theerthams on the Tirumala Hills... you can also visit few more temples in Tirupati including "Govindarajulu Temple", "Srinivasa Mangapuram", "Padmavati ammavari Temple, Tiruchanur" and ISKON Temple. If you have time, you can visit "Sri Kalahasthi Temple" (known as Dhakshina Kailasam) @ 35km from Tirupati and "Kanipakam Vinayaka Temple" @65km.. since you are planning to go in March/April, pls note : that being the post examination & early days of summer vacations, will be over crowded - be prepared for longer ques. summer will be too hot in that region. Pls take care of yourself.. Be hydrated...
Akasa ganga, kapila thirdam, sila thoranam, and many small temples in tirumala, you can board A devasthanam bus or you will find vehicles which will take you to all the places mentioned. Govinda swamy temple, Aliveru manga devi temple in tirupati. if u have time u could visit sri puram temple known as Golden temple which is A 3 hour drive from tirupati