what is the best way forwards when a P&ID drawing beomes increasingly dense with information ?
1. is it wise to split it into two sheets ? (what problems are there if they are split, i.e. speed of access, numbering of documents etc)
2. using a block to replace repetitive functional blocks, and show this block else where for detailed description ?
(i.e. pump 1, pump 2 etc all inside a small block, and the functional block for pump explained else where for reference)
If these two aren't good enough, what other solutions are there for higly dense P&IDs ?
Go with Option 1.
Don't worry about the points you noted down. This is exactly why AutoCAD P&ID is here. to solve all those issues for you.