- No, size doesn't matter - grace matters.
- No, transubstantiation doesn't require an altar.
- No, it's not that organized.
- Depends, relics cannot be sold so they either have to be retired and buried or go to other homes. It would be up to the local Bishop to deal with storage of the altar relic. But Canon Law says the altar can lose its dedication
Can. 1212 Sacred places lose their dedication or blessing if they have been destroyed in large part, or have been turned over permanently to profane use by decree of the competent ordinary or in fact.
- No database and no correlation - the relics are not necessarily related to the saint of the Church (i.e. Our Lady and St. Joseph have no 1st degree relics, so they couldn't have churches dedicated to them if that were the case). If you want to find out whose relics are at an altar, you'd have to ask someone at a parish. I have no knowledge of any of the relics of any of the churches I go to, which is kind of sad, but might give you some indication of how important the relics are to average Catholics, it might be another "one of those things", so I wouldn't get hung up about it if I weren't a Catholic - we've got plenty of other weird stuff to worry about going on in the Church!
Also, the degrees of relics are:
1st degree
Any body part, hair or blood from the saint
2nd degree
Something that the saint touched or used during their lifetime. Saints like St. Maximillian Kolbe, who was cremated at Auschwitz, and St. Anthony of Egypt, who was buried in secret so his body wouldn't be fought over, only have 2nd degree relics.
3rd degree
Something touched to a saints grave or over their corpse.