You need neither a tach nor a shift indicator (seriously!). For new riders especially, it's better to ride without depending on one, because it forces you to feel what your machine is doing.Lots of new riders like to overthink things and pay way too much attention to RPM....and you can't ride like that. It has to be instinctive. And it will become that way if you practice it.
Don't ride by numbers, you will be a menace to yourself and others if you are constantly looking at the tach. Looking at your instrument panel means taking your eyes off the road. It is something you should only do when you have a piece of straight clear road where you can afford to take your eyes off the road to check your speed/RPM.
Best advice: don’t over-rev, shift up early. If you up-shift too early, you will know, the bike won’t accelerate fast enough and may even buck.
You must learn to ride by sound and by the way the bike feels under your butt. That takes practice, you’ll eventually know the power ban of your particular machine and where it purrs.
Safe riding.