>Do i need to add repeaters for that , if yes after how many slaves
I assume you will be using RS485 interface.
This can support a maximum of 31 slaves (and one master) per network segment.
So you would need to have 4 networks to implement this. Each network will have one master and up to 31 slaves. I do not understand your reference to repeaters in this context. Repeaters normally just extend network distances. They do not increase the number of supported slaves in a network segment.

>can i fetch this much data as mentioned above per seconds or it will cause delays
6 data points equates to 12 bytes, so a very small amount of data.
Given that there is a maximum of 31 slave devices per network, I cannot see that there would be an issue with delays for this small amount of data.

>do i need to add more CM1241 Module or single module will serve the purpose.
Yes you will. The CM1241 module only has one interface, which will support  a maximum of 1 master and 31 slaves. To support 100 slaves, you will need 4 network segments and thus 4 CM1241 modules. Each interface will need its own PLC code.

>as an alternate solution what if i connect 10 modbus RTU Slaves to each external gateway >(Modbus RTU to Modbus TCP converter) and in the end attaching 10 gateways to s71200
That would work and you would avoid the need for the CM1241 modules. You would need some different PLC software blocks though, as the Modbus RTU blocks would not work. You would need the Modbus TCP client (master) blocks. You will need 10 instances of the MODBUS_CLIENT block as each one will need to open a separate connection to each gateway, as each gateway will have a its own IP address. The disadvantage of this method is that you have to use 3rd party hardware (the gateway convertors), which will need programming. I have done similar in the past, and we have suffered issues when gateway spares are sent out. It is not unknown for non-programmed ones to be sent out due to out of hours staff just grabbing a spare from the inventory.

I hope this helps.

Every commercial repeater I've seen has also been an isolator, which is the good side of repeaters.

One issue with using a repeater is that a repeater extends a 485 network segment from x number of slaves (upstream of the repeater) to x + n number of slaves (upstream and downstream), which increases the total polling time for that segment.

This TI app note, AN-1057 Ten Ways to Bulletproof RS-485 Interfaces is targeted at designers, but it shows that TI has developed 485 chips designed specifically to handle repeater operations
https://www.ti.com/lit/an/snla049b/snla049b.pdf?ts=1727877689783&ref_url=https%253A%252F%252Fwww.google.com%252F

The longer the daisy chain, the more devices that can be affected by a fault.   Be aware that with daisy chained (all devices paralleled) wiring, the physical disconnection of wiring at one upstream slave can open the 485 daisy chain and 'kill' communications to all downstream devices.