What are the origins of the following Old-Rite practices:

Spelling of Jesus: Ісусъ [Isus]

Creed: рожденна, а не сотворенна (begotten but not
made); И в Дѹха Свѧтаго, Господа истиннаго
и Животворѧщаго (And in the Holy Spirit, the
True Lord and Giver of Life)

Sign of the Cross: Two fingers, pointer finger straight, middle
finger bent

Number of Prosphora
in the Liturgy and
Artoclasia: Seven Prosphora

Direction of
Procession: Sunwise (circle left-to-right)

Alleluia: Аллилуїa, аллилуїa, слава Тебѣ, Боже (twice
alleluia, glory to Thee, o God)

I'm no expert but I think that the origins are Greek. Patriarch Nikon wanted to adjust them to contemporary Byzantine practices he perceived original, but actually the Russian practice (taken once from the Greeks) that the Old Rite maintains was "more original". But I may be wrong.

Yes I know that much, but I am looking for verifiable sources such as the writings of various Church Fathers.

Much of the problem has to do with the difficulty of gaining access to the (presumably) relevant Greek manuscripts. The ones in Italy are accessible, but the ones held by the Ecumenical Patriarchate are not. Still, one can learn quite a lot from pre-revolutionary books giving detailed history of liturgical texts, and by comparing the present Greek editions, the Nikonian editions, and the Old-Rite editions.

All this requires linguistic ability, naturally.

Fr. Serge

If the Ecumenical Patriarchate has nothing to hide then why do thy make gaining access to the relevant Greek manuscripts so difficult.

A reasonable question, to put it mildly. Having never had access to the library/archive of the Patriarchate, I don't know what it is they are guarding - but it's not just a matter of the pre-Nikonian Liturgy; there are quite a number of other questions whose answers might well be in that collection.

Fr. Serge

Probably Greeks are wary of allowing Western scholars access to precious materials. They have had experience of the pilfering of valuable manuscripts by people whom you would not expect to stoop to theft... but the temptation seems irresitable......

It's not ture.Seven prosphora for liturgy,YES. for artoklasia,NO.Old rite also use FIVE for artoklasia.

Strictly speaking, the Old Rite simply retains the texts and customs of the Russian Church prior to the Nikonian reform; there are few if any practices invented by and unique to the Old-Ritualists.

Fr. Serge

While it might be difficult to gain entry into the Ecumenical Patriarchate's library, it is not the case for the wonderful library in the monastery of Mount Sinai.

I have been through it; one must merely ask one of the monks for a book. The very old documents and scrolls they may prefer to handle themselves, though.

Of course, you have to get there first, though!

Alas, I have not been to Mt. Sinai and at my age in in my arthritic condition I am not planning to go there. So someone else will have to go and compare old Greek texts with pre-Nikonian Church-Slavonic texts.

Fr. Serge