Questions About Prestige Classes [5E]

[PapaQuackers]

Hey guys, with the recent revised subclasses released from the UA (namely the Kensai), I've been working on a prestige class for Fighter/Monk (Kensai) hybrids.

I just had a couple questions about prestige classes in 5E, namely:

1. What should I be doing for the proficiency bonus for 10 levels?
2. How tightly packed should a prestige class be in 5E?
3. Should I be balancing a prestige class around the idea that they'll be taking all 10 levels in it, or sort of expect them to take a few and then peter off?

[noob]

Well in 5E since multiclassing have so few penalties if you have a prc that grants enough cool stuff for casters on the two first levels then some people will dip in it.(heck there is even some wizards who take two fighter levels)
So if you put cool stuff on the two first levels except people to possibly dip into it.

[Yuki Akuma]

Proficiency bonus is determined by all of your levels added together, so a prestige class would - and should - do absolutely nothing to affect it.

[PapaQuackers]

But what would be the proficiency bonus per level?

[Arkhios]

Currently the only semi-official prestige class iteration we have is the Rune Scribe, which requires the character...
...to be at least 5th level before taking levels in Rune Scribe
...to have at least 13 in dexterity and intelligence
...to have accomplished something special in order to become a rune scribe

A Rune Scribe has up to 5 levels, which is where I would personally keep any prestige class levels. Only give the abilities that really matter, and leave the rest out.
Also, I would follow the above pattern when designing prerequisites.

As for the proficiency bonuses, well, since taking up levels in prestige class is essentially via multiclassing, the proficiency bonuses should be equal to any other class when multiclassing: depend on your whole level. You can find the Character Advancement table from Player's Handbook, page 15.

PS. It shouldn't be that hard to see the pattern, since the proficiency bonus starts from +2 for the first 4 levels, then increases by one at 5th, 9th, 13th, and 17th, so that the value changes for four levels each;