hey Vivek. this is off topic for this channel as it's a discussion about compose web. but i'll keep it in a context of compose web for those new here.
the tldr is:
web is nothing more than yet an other client you can cater for, similar to android and ios.
so the same way of implementing things for mobile is the same on web, but instead of dealing with android OS and iOS, you are dealing with the browser (javascript APIs).
re push notifications and payments, you said you are dealing with android and ios. how are you handling/going to handle it there? if you are using a 3rd party solution, check if they support browsers as well and you are good to go.
if they don't support all 3 clients of yours, you can go ahead and implement it manually on the backend. you have full control there, but that's a different topic on its own.
everything else is something no one else can answer for you. no one knows your skillsets and your situation and 'should i use kotlin' is such a generic question to answer. this is a kotlin specific slack channel, so 'yes. use kotlin' is not very helpful