> 5 Volts only I set the limit

Let's see, how many things have I blown up with 5V ?   ;-))

> I have now a microlab pic kit #1 and wondered how I might
> improve the led and the well monitor using this and at last do
> something useful with the outcome

PICKit1 is good, so you have a range of PICs available to use
(I don't believe it does 18F though)

Code for what you want to do would be fairly straight-forward.
LCD is probably (perceived as) the only tricky bit, but it's not
that difficult. Ten I/O for the display (8-bit mode data, RS, En),
one for the sensor, leaving two for buttons/switches. LCD data
lines can be used as well when the LCD isn't being addressed,
perhaps to log usage or transmit data to a remote (have you
considered a radio link ?)

That said though, what type of LCD do you plan to use ? 16x1,
16x2 etc alphanumeric or discrete numerals (eg glass panel)

Speed isn't a big issue, you could go crystal or RC. Here's a
plot of RC values, something close to 4MHz would do

http://home.clear.net.nz/pages/joecolquitt/0f84rc.html

Crystal would be more convenient and much less fuss though if
you don't have access to a frequency meter

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