The Bluetooth Classic has a limitation of 7 slave devices in a piconet and they are time and hop synchronized to the master ( ie master and slaves share a common physical channel and it is not possible to address more than seven slaves for a master when in Active mode). In BLE each connection from a master to a slave operates in an independent physical channel( ie LE slaves does not share a common physical channel with the master), hence there is no limitation imposed by the Specification except as specified by the Connection interval and slave latency rules ( Note that individual bluetooth controller manufacturers may decide to limit the number of connections depending on the practical bandwidth limitation). please see the Bluetooth Classic vs Bluetooth Low energy Topology below.
Is it possible to achieve the multiple sensors ( BLE) and Headset (BT classic) connected to mobile? Yes it is very much possible, except that there are some BT4.0 controllers which doesn't allow LE advertisement while connected to another BLE device. please check the known limitations in a particular bluetooth controller.