Why do you have to count Sefira standing up ?[Sh"tz 489-7]
1) All brochos on mitzvos have to be done standing.
2)We have an asmachta (a refrence) from a Pasuk ("Mei'Hocheil chermeish ba'kamah") to do so.
If someone said the bracha sitting,what's the Halacha? What about if he said the Sefira itself sitting ?[M"B 489-6]
In both cases he is Yotzei B'Dieved.
Why should Sefira be counted before A'leinu ?[M"B 489-2]
To say it as early as possible, to be "m'kayeim" -"Temimos" (full days).
We know that everyone is supposed to count Sefira for themslves,[from the Pasuk "U'sefaartem lo'chem"]; Can someone be "motzei " you with the bracha ?[M"B 489-5]
Yes, but the Minhag is for everyone to make the bracha themselves (when possible).
If you count Sefira in Lashon Kodesh do you need to understand what you're saying ?[M"B 489-5]
If someone only counted the amount of days & not weeks (i:e Today is the 20th day of the Omer ) can he continue counting with a bracha on the following nights ?M"B 489-7]
What if he only counted the weeks (i:e on day 14 he says,"Today is 2 weeks in the Omer)?[ibid]
Why do we say "Harachamon or Y'he Ratzon Sh'Yiboneh.. afterb counting? [M"B 489-10]
To daven that we should be "m'kayim" the mitzvah of Omer in the Bais HaMikdash.
If someone counted by saying," Today is day 13 minus 1, is he Yotzeh ?[M"B 489]
How come we don't say Shehechiyanu on Sefiras HaOmer ?[A"H 489-5]
We only say Shehechiyanu when it contains Simcha, (that is why there are problems with an Avel saying Shehechiyanu), unfortunately by Sefira we have "tzar" that the Bais HaMikdash is destoyed & we can't actually bring the Korbon Omer.
What's the reason someone keeping the 1st 33/34 days of Sefira can shave (take haircut) tommorrow ?
Since there's the double simcha of Shabbos & Rosh Chodesh.
If someone said "ches" instead of "shemona" is he Yotzei ?[A"H 489-9]
If someone wrote down what number the Omer is, is he Yotzei ?[A"H 489-9]
Can you make a bracha without knowing what day of sefira it is, figuring you'll hear it from the person next to you?[SH"A 489-6]Answer: Not l'chatchila.
If someone isn't sure whether or not he counted Sefira the day before (meaning day & night )the Halacha is, he can continue counting with a bracha. Why ?[M"B 489-38]
It is a s'fek sfeika; Firstly, maybe he didn't skip yesterday [thereby allowing him to continue with a bracha], & even if he did skip maybe the halacha is like the Poskim that say each day is an independent Mitzvah [thereby requiring it's bracha].
When is a Chasuna (wedding) permitted during the Aveilus period of Sefira ?[M"B 493-1]
When someone remarries a woman he divorced.[There is not the simcha of newness. This is also why such a person has to go to battle, unlike another person in their 1st year of marriage (even when it's their 2nd marriage).
What is the reason that under the right circumstances a Posek can give someone a Heter to shave [i:e he will lose his parnasa ?[IG"M]
Since aveilus during Sefira is a Minhag [albeit a strong one ] it wasn't undertaken for circumstances that will cause financial loss. Whereas, the aveilus during the week of Tisha B'Av is a Din & therefore different.