Re: engagement ring - who puts it on?
Ha! Sometimes I can’t believe the things us desis do in the name of Islam and culture. They are perfectly fine with having a engagement party or other wedding events where the bride and groom sit together before the Nikah and are usually sat very close to each other but still find it necessary to exchange rings through the elders like WTF! You are fine with them sitting together, where they are bound to touch each other either purposely or by mistake! 
Oh and the very obvious thing since when has having engagements, mehndis and shaadis parties the way we have allowed in Islam. Either follow it or don’t contradict it in the same event. I mean seriously!!!