I think this was a very well reasoned argument. I would just differ on a couple of small details.
1. He had to be crucified on Passover. One day before wasn't close enough for him to be "our passover is sacrificed for us" (1 Co 5:7)
2. Your article makes the supposition that the lambs were killed before Nisan 14, on the afternoon of Nisan 13.
Exo 12:6 And ye shall keep it up until the fourteenth day of the same month: and the whole assembly of the congregation of Israel shall kill it in the evening.
You stated that Jewish tradition said the lambs were killed at 3 PM on the 13th. This would seem to violate Gods command. It hinges on the word "evening". I believe if you do a study on this word, you'll find that it must pertain to the time period after the sunsets, or just after the sunsets, but surely not in the afternoon.
3. Is Passover a sabbath biblically?
Lev 23:5 In the fourteenth [day] of the first month at even [is] the LORD'S passover.
Notice that there is no injunction against working.
Lev 23:6 And on the fifteenth day of the same month [is] the feast of unleavened bread unto the LORD: seven days ye must eat unleavened bread.
Lev 23:7 In the first day ye shall have an holy convocation: ye shall do no servile work therein.
These verses are linked. Unleavened bread begins the 15th and being the first day of unleavened bread, it's a sabbath, a day of rest.
Lev 23:8 But ye shall offer an offering made by fire unto the LORD seven days: in the seventh day [is] an holy convocation: ye shall do no servile work [therein].
As is the last day.
So how does this fit in? Jesus had his passover meal with the disciples on Tuesday night, just after sunset, the time when the lambs would have been slain. He instituted two new ordinances and TOLD us that the bread represents his body, and the wine his shed blood. He did this at the same time the lambs were to be killed.
He died on passover at around 3 pm Wednesday and had to be buried before the sabbath of the first day of unleavened bread started because it wasn't legal to bury corpses on the sabbath. He was entombed just before sunset.
As you said, he HAD to be in the grave 3 days and 3 nights or else he was not the messiah. It was the only sign that told us that he would be:
Mat 12:39 But he answered and said unto them, An evil and adulterous generation seeketh after a sign; and there shall no sign be given to it, but the sign of the prophet Jonas:
Mat 12:40 For as Jonas was three days and three nights in the whale's belly; so shall the Son of man be three days and three nights in the heart of the earth.
Anyways, I think these are relatively minor points and I congratulate you on proving the truth for yourself.