Hi,
Sadly you don't give values...so it's just a theoretical discussion.
But the answers differ very widly according your application.
While with an audio ADC the exact value isn'very important ... here the noise is more important.
But if you want to design a highly accurate, high resolution measurement device...then it becomes difficult.
Low drift, low noise, high accuracy....
10 bits accuracy is easy
12 bits accuracy ... you have to care about some things
14 bits accuracy ... becomes difficult if you don't already have good knowledge and experience in designing precision analog circuits
16 bits accuracy ... is difficult even for experienced designers
18 bits accuracy ... needs very, very good design, and every resistor, Opamp, reference needs to be chosen very precisely...it becomes expensive
20 bits accuracy is about impossible to achieve....
******
Should I find a voltage reference with that exact output?
Some desingners do this. I say: there is no need to.
Choosing a 4.096V reference instead of a 5.000V reference just reduces performance by max 1.7dB...
Additionally.... often you need Opamps for signal conditioning...if your ADC input goes up to 5V, thdn you need an extra power supply fir the Opamp with higher voltage than 5.0V.
Even with good rail-to-rail Opamp I recommend to leave some margin (supply voltage to output voltage) to avoid clipping and to avoid that the Opamp goes into saturation - even for a short time, like an signal overshot.
1) I don't say bad practice. But often the ADC reference inputs need a very low impedance source ... this usually can't be guaranteed with a voltage divider.
2a) in any case I recommend to use a capacitor very close to the ADC_VRef_input
2b) true, drift needs to be calculated. But if you use good resistors from the same production batch, then they should have very matching tc. But ratio is limited to 1:1, 2:1, 3:1...
2c) see answer to 1). Often you can't do without Opamp.
Klaus