Lyb
“First, According to those that are saying that kiddush you shod be Machmir with the shiur, then you should be machmir every Friday night.”
Agreed. but see below
“Second, in Shulchan aruch it only mentions a machlokes regarding the kzayis for matzah, … But nowhere does it mention to be machmir by a kos,if it is a doyraysa kos, to use the bigger shiur.”
Why would it be different? When you are unsure/have machlokes regardign shiurim by Deorisa’s me machmir and d’rabanas be meikel. Why would there be a difference between MAtzah and Ksosos?
” If your are machmir to use the biggest shiur by mitzvos in general, then be machmir by the first kis as well. If your not usually machmir in general for the bigger shiur in mitzvos than you won’t have to be machmir here.”
By defintion you never “have to be machmir” If a person wants to be machmir with some mitzvas and not others tovoi alav bracha! Why is it all or nothing? (Especialy given the aformentioned distinction between Deoraysa and Drbanan)
“If your going to want to use the Chazon Ish’s shita for the first kos, you might as well wear the long tzitzis all year round”
Wait what? Mai Inyan shmita Eitzel Har Sinai? How did you even make the conecion MAtzah to tzitizis? A person want to be machmir with a mitzva that is chaviv and comes once a week (or once a year if only PEsach he is makpid, or even once every 3.5 years if he is makpid only when the first night PEsach is Shabbos) Would you say no first get bigger Tzitzis?