For your questions:
1) Yes you can taste, but most liquids require steeping aka just sitting there, getting a shake now and then, and squeezing the air out for the alcohols to be removed (which can give liquids a bad aftertaste) once of twice in the fist few days.
Some liquids are fine right away after being shaken but won't be as good as can be. SOme take about a week, others up to 3 weeks.
You can accelerate this process a few ways, but at a possible bit of a loss of quality. Microwaving for 5-10 seconds is one, but not very popular but does work a bit. Using ultrasonic cleaners to vibrate the liquid can take days off the steeping period. Using a small blender can also work, but ensure that it's sanitized/100% clean as you need to transfer into the bottles after.
Just remember to ventilate your liquids at least twice in the first few days,BEFORE you shake the bottles. Shake them vigorously until you see a uniform amount of air bubbles throughout.
2) unless you really need to be crazy accurate as if it's the end of the world, just use any technique that works for you.. I use drops for single bottles, measuring cylinders for large batches. Lot easier than the math involved with balances, and the cleanup is a big whoopee-doo of a 5 seconds rinsing of the cylinders. As many flavouring comes in PG (unless stated otherwise), the difference is again, quite small. I use 50/50 base and it's never been an issue once.
I've redone recipes many times, and not once did my off-side mixing methods done anything wrong or bad... they always have come out just fine.
Do go get the calculator though to have the guidance for quantities, and check out e-recipe sites for percentage for the flavours, recommended percentages for alone or in mixes.
Here's what I use, but there's plenty of others out there:
eJuice Me Up - Best eJuice Calculator
http://..................../
Have fun!