Need to purchase/rent a Wifi modem/router for existing BSNL Broadband connection for 2-3 months temporary period. Please help with suggestions.

Current Setup:
Desktop PC
ZTE ZXDSL 831AII modem(without wifi) purchased from BSNL in 2008 use it via USB.
Placed in 1st floor Corner room.

Temporary Planned setup:
Desktop, laptop & smartphone.

1. Do I just need a wifi modem or both modem + router?

2. Will buying wifi unit from BSNL would be better option or renting it? And why?

3. Are there any BSNL users here from Gujarat? If yes, any idea which wifi model BSNL is giving to users these days?