Those are interesting questions, best answered by a network engineer.
On the topic of priority, some cells seen by the modem will likely have a higher priority than others (in terms of whether they should be selected).
These priorities are often visible in the AT+QENG="neighbourcell"
results:
AT+QENG=“neighbourcell”
+QENG: “neighbourcell intra”,“LTE”,100,69,-12,-116,-82,0,23,6,30,22,255
+QENG: “neighbourcell intra”,“LTE”,100,47,-10,-114,-95,0,26,6,30,22,255
+QENG: “neighbourcell intra”,“LTE”,100,46,-19,-123,-95,0,16,6,30,22,255
+QENG: “neighbourcell inter”,“LTE”,3148,189,-12,-120,-100,0,23,4,22,26
+QENG: “neighbourcell inter”,“LTE”,3148,496,-18,-127,-100,0,23,4,22,26
+QENG: “neighbourcell inter”,“LTE”,1250,411,-11,-111,-88,0,26,5,18,20
+QENG: “neighbourcell inter”,“LTE”,1250,83,-16,-113,-88,0,26,5,18,20
+QENG: “neighbourcell inter”,“LTE”,1250,298,-20,-118,-88,0,26,5,18,20
+QENG: “neighbourcell inter”,“LTE”,1250,167,-18,-115,-87,0,26,5,18,20
+QENG: “neighbourcell inter”,“LTE”,9410,202,-13,-95,-73,0,16,5,16,20
+QENG: “neighbourcell inter”,“LTE”,9410,136,-17,-99,-73,0,16,5,16,20
OK
A larger number (highlighted) is a higher priority.
EARFCN 100 is on B1, 3148 is on B7, 1250 is on B3 and 9410 is on B28.
Signal strength and quality are also major factors in selecting cells.