Hey welcome to the forum. You will need a one star cert to be able to rent any sit-in kayak from any rental station (PA Water Venture, SCF Paddle Lodge). If you intend to own a sit-in and be able to apply to kayak out to the islands, then they will ask for you to be certified higher. You can refer to SCF website for more details on certification.
Especially now, with new reservoirs opening up for access, like Pandan Reservoir, any kayaker wanting to paddle in a sit-in kayak will be subjected to checks by the appointed operator at the reservoirs (SCF, PA Water Venture). However, no such rules need apply for sit-on-tops (open cockpit), which you can rent from the operator, without need to have a star certification.
Hope this helps.