I agree with imba, doing a fishless cycle is way less stressful for you and your fish.
Especially if you haven't kept fish for a long time or don't understand the cycle perfectly, cycling with fish mostly ends in disaster.
I wouldnt do Tiger Barbs in a 20. They get way too big and are way too active. If you do, you can really only do a few and no other fish, period. And you'll probably have aggression issues with them as they really do better in large schools. Skip the TB's, it'll save you a ton of headache.
None. Itll be WAY less work to use ammonia to cycle the tank. If you HAVE to do a fish-in cycle it will take way more work and way longer to cycle due to constant water changes to keep ammonia and nitrites safe for your fish.
What exactly is the set up you're running currently? Filter? Heater? Plants?
I'd do a fishless cycle, fish in cycles are harder to control and super stressful if you don't know exactly what you're doing.
Yes, it takes more time to have fun and see fish swimming around, but you'll be happier with it in the long run.