if you do not advance your level after you level up, will the world stay at the read level number on the screen, or t he technical experience advancement, tucked away unutilized.

i am level 1 I have leveled up to level 2.. I do not advance to level 2... does world stay at level 1 until I am level 50 and decide to advance?

the experience does continue to add up even if it shows the bar as full before you level up so for example if you forget to level up you can end up leveling up several times when you finally decide to do so.

Yes.

There is an advantage in not leveling up, if you are interested in that kind of thing. By not leveling, it is possible to level your combat skills up to 100 while your character is still level 1.

Because the enemies you face are mostly the same level as your character, your character's combat skills will greatly exceed the combat skills of your enemies.

Do with this information what you will.