I use inserts as standard configuration in several of my bass models, have been using them for many years now, and would suggest you utilize either stainless inserts or (my preference) hardened steel inserts instead of the die cast zinc (or even worse - brass) units you linked to in your other thread
after experimenting with numerous different styles of inserts, here's the style of hardened steel inserts I have found to be the most reliable (these have a 10-24 internal thread)
two inserts would probably work OK, but I'd recommend utilizing four unless you have some physical constraint keeping you from it.
I'm also of the mindset that utilizing your drillpress to hand-turn the insert into the neck heel is the optimal workflow to use. Doing so allows you the be certain that you thread the insert into the hole so that it's perpendicular to the heel surface and not at an angle (even hard Maple will give enough to allow your insert to thread into the neck at an angle, requiring you back the insert out, plug the hole, and re-dril for another attempt at installing it correctly - unfortunately I do know this from first-hand experience

)
installation is easiest when done prior to shaping your fingerboard, but since you note that you're using a pre-made neck you don't have this option. I recommend you take the time to find a means to secure the neck onto the drillpress plate so that the heel remains parallel to the plate and perpendicular to the Forstner bit you'll be using to drill the pilot hole - even when the neck is under pressure - since you'll need to apply firm pressure when threading the insert into the neck shaft. I guarantee you that you DON'T want your neck shifting on you while you're installing an insert
best of success on your project!
all the best,
R