What is the maximum number of simultaneous Bluetooth connection I can make for LWB5+?

Ideally, you can connect upto 15 BT devices but the constraints are memory limit, connection parameters including connection interval, length of connection event, etc. 
 
For example, if we have multiple LE connections which are all with connection interval of 40ms and each connection's connection event is with 4 pairs of Tx/Rx, i.e. 5ms CE, then the max no. of LE connections will be 40/5=8. If  you need to do something else at the same time, such as maintaining a SCO connection, doing advertisement, etc. then you will definitely have less than 8 even for the LE connection with the same connection parameters.