Can I use this chainring with a Shimano 11-speed chain?

Technically yes - Shimano 11-speed chains are compatible in width with SRAM 11-speed systems, though SRAM recommends SRAM chains for optimal X-Sync tooth engagement.

What bottom bracket do I need for a GXP crank with this chainring?

The chainring mounts to the 110 BCD 5-arm spider independently of the bottom bracket. GXP cranks use SRAM GXP bottom brackets (threaded BSA or press-fit PF30) depending on your frame.

Is the 40T tooth count listed the only available variant?

The 40T is the listed variant at Rs 7310 on InstaSport. Other tooth counts (38, 42, 44, 46, 48, 50T) exist in the SRAM range - contact InstaSport support for availability.

SRAM

Sram Chain ring Road 1X11 Speed 110 BCD

Name: Sram Chain ring Road 1X11 Speed 110 BCD
Brand: SRAM
SKU: CMB_LONGSHINE_11.6218.019.003
Price: 7310.00 INR
Availability: InStock
Author: InstaSport Editorial

₹7310.00

Description

Specifications Application : Road, Cyclocross. Mount : 110 mm bolt circle diameter, 5-arm. Teeth : 38, 40, 42, 44, 46, 48, 50. Gearing : 1x11-speed. Technical Information Material : Aluminium. Compatibility Force 1 Rival 1 CX 1 BB30 GXP Features Mud recess. A component of the SRAM 1x™ drivetrain. CN