The next four sections touch on important particulars in the ritual, the planning, and the record-keeping. GICI 26 treats the needs of the baptismal rites and the pastoral accommodation for those celebrating.
26. In the celebration the parts of the rite that are to be celebrated outside the baptistery should be carried out in different areas of the church that most conveniently suit the size of the congregation and the several parts of the baptismal liturgy. When the baptistery cannot accommodate all the catechumens and the congregation, the parts of the rite that are customarily celebrated inside the baptistery may be transferred to some other suitable area of the church.
The priorities for locating good baptismal liturgy: first, the size of the congregation, and second, the appropriateness for the rite. This is not something that can be legislated easily within a diocese. And even in a parish, I could see two or more possible solutions.
The bottom line is that the water bath must take place in the font. Within the bounds of good sense for good liturgy, everything else is up for reasonable discernment.
My sense of what would be needed for a baptistery or a baptism area of a church would be flexible seating for those who choose to sit or must sit for parts of the rite. A baptistery would seem to need an ambo, even a portable one. In a church in which the celebrants of baptism would be on the move, easy access via aisles and open spaces between the Liturgy of the Word, the baptismal rites, and the concluding rituals. Many places move people from ambo to font to altar. A question for pastoral musicians: what sort of processional music would or should be provided?
Chapels and small churches are more likely to have these three locations in one place. A good presider would attempt to use a bit of silence to mark the main liturgies of the baptismal rites.
Regarding adult catechumens at the Easter Vigil, in a church in which the congregation could not fit into or see the baptistery, I would presume the water bath would take place at the font. The accompanying rituals of light (and possible the robing in white) would wait a return to the church.