Tomid B'simcha

Daf of the week

R.Noson Sternhartz wrote that R. Nachman Breslover said ,

"Mitzvah Gedolah Liyhos B’simcha Tomid."

1)  What makes this a mitzvah?      None of the monei hamitzvohs

count this as a mitzvah.  It is true , that mitzvahs should be done

besimcha. This is a way to do the mitzvah but not a mitzvah in itself.

2)  How can you say “Tomid” if there are times when not only

is it not a mitzvah but an aveirah ?

In Hl Aveilos # 391 – 1  Aveil  asur liyhos b’simcha .

3)  Why is this, a mitzvah gedola and other mitzvahs are not gedola?

I found only one mitzvah gedola in the whole Shulchan Aruch  

“Mitzvah gedola l’haspid hameis  koroui” ( It is a great mitzvah to eulogize

a niftar properly).

There is one more mitzvah where gedola is mentioned

Hl. Pidyon Sh’vuyim “ein lecho mitzvah gedola k’pidyon sh’vuyim.

PS. I have no answer to the questions,

 Yehi ratzon, the day of "B'simcha Tomid" should arrive b'karov mamash.