Try switching to de-caff coffee/tea. Honestly, buy a nice brand and you won't taste the difference. Even DH drinks de-caff now (although he doesn't know he does) and has never once complained, not even the first change over cup of coffee type thing. Just don't opt for the supermarket cheepie, I'm sure that's a little different?
1) Yes you can drink tap water
2) Sweetners have already been prooved to be bad for adult consuption, they contain ingredients heavily linked to things such as Parkinsons Disease and certain cancers. I'd not use sweetners during pregnancy based on simply knowing that, you have no idea (if it can do that to an adult) what they might do to a growing baby. Certain sweetners are supposed to be 'ok' while pregnant, others are on the "No" list while pregnant. Do some reasearch if you want to continue using them but honestly you are far better using sugar.
3) Yes you can eat quorn, that's fine.