I'm trying to make a few enhancements
I would suggest a few changes:
1) the prescaler can be done with something simpler / faster, like MB506 or MC100EL family of counters -> those guys go all the way to Ghz.
2) you may want to think about if you want to read prescalers. It adds to some hardware complexity and lots of software complexity.
3) input signal conditioner: may be a few gates connected as linear amplifier.
using the 3V version of this oscillator,
A few options:
1) you can run the 3v oscillator at 5v - I have done that for many oscillators, and TCO-919 most recently;
2) you can run the pic at 3v. The lcd can still run at 5v or you can use a charge pump to create a negative voltage to drive the contrast.
3) even if you run the oscillator at 3v and the pic at 5v, they are likely to work gotether.
4) if not, run the oscillator's output through a not/nand gate + feedback resistors and call it a day. See my TCO-919 thread - the Vpp there is less than 100mv or even smaller, as I recall.