I have two hopefully simple questions. First, where is a good location to connect the supply line for the toilets? I have a mid 60’s split-level and I replaced all the copper supply lines but have not yet connected the upstairs toilets. I heard/read somewhere that the line should be connected at a point so that when the toilet is flushed it will NOT pull cold water from the shower/tub while it is in use. The original line was tapped off the shower cold supply and fed two toilets, though I don’t recall a problem with that setup. I still have access to all the pipes. Number two-what is the recommended pipe size to feed outside hose bibs? The plumbing books I have say use ¾”. The house originally used ½” and I have friends with relatively new houses that use ½”. Thanks.

Standard house piping calls for a 3/4" house main and 1/2" branches with no more then 3 fixtures connected to a 1/2" branch.
If it's too late to run a dedicated 1/2" supply off the 3/4" main then I would run a 1/2" branch for both toilets off the 3/4" main. That way nobody gets parboiled in the shower when someone flushes the john.

As for the hose bib. Up until recently we supplied all our hose bibs with 1/2".
Now code calls for a 3/4" supply, however, I can see no advantage to changing over if your hose bib's already supplied with 1/2".
Regards, Tom