Part 1
There are many reasons why the medieval development of the altar as wall with a tabernacle as its center piece was not fortuitous. 

The most important has to do with our conception of the Eucharist as PRIMARILY (1) sacred food and drink, or (2) an object of adoration. 

The essence of Eucharist in scripture is sacred food. Jesus confected the Eurcharist at the Last Supper at the dinner table, and commanded us to both eat and drink. For most of the first thousand years, our churches faithfully conveyed that original divine intent with an altar that was instantly recognizable as a dinner table, to which bread and wine were brought, and from with the body and blood of Christ was distributed as sacred food and drink in the form of bread and wine. The original scriptural word that was adopted for a church building was "ekklesia," which means "gathering" and which came to be understood as the "place of gathering." Its Jewish predecessor was the synagogue (essentially same meaning).