Stocking my 20 gallon and adding fish

[Leopardfire]

I have a few questions to ask before I stock my tank. I may have asked some of these before, but I need to be absolutely sure on everything because I can't afford to mess up again.
My 20 gallon long aquarium just finished cycling after 2 weeks. I never saw any nitrites and the nitrates are only at 2ppm, but it consistently breaks down 3ppm ammonia in 24 hours, so I think it's ready for fish. I want to add 6 corydoras, 6 harlequin rasboras, and 1 betta. Is this tank load ok for my tank, or will I be overstocked.

Also, how should I add my fish into the tank? Should I add 6 of the fish and then wait a week and add the rest except for my betta? Does it matter if I add the cories or the rasboras first? I was planning on adding the cories first but I need to make sure that's ok.
Is there a chance the other fish will hurt my betta if I add him last? I don't want them to form territories and beat up my betta when I add him later.

Finally, my tap ph is at 8.2. Will the fish be able to adapt to this? I know there's ways to lower ph, but I'm not experienced with fish and I don't want to get into that.
I know it's a lot of questions, but thanks for answering.

[ChoclateBetta]

Guppies.

[Olympia]

Personally, I would add the 6 rasbora first and wait a week or two. The rasbora are more hardy than the cories and will do better in a freshly cycled tank. Then you can either add the betta or the cories, it should really matter as these two don't really compete for territories. Neither fish should hurt the betta as they aren't territorial. However you should still watch the betta for aggression.
The pH is high for these species, yes, but they should do fine. The rasbora may seem pale though..

[Leopardfire]

Thanks for the advice, I will get the rasboras tomorrow. My betta has lived with cories before and he was docile so I don't think he'll be aggressive now. I'm so excited that my tank will finally be ready!!!

Also, is it odd that I have only 5ppm nitrates after a cycle? I haven't heard of that anywhere.

[Olympia]

Is the tank planted?

[Leopardfire]

My tank currently has 3 small plants, but it will be moderately planted when I get fish. I think the plants it has are white ribbon grass and 1 anubias. The grass is dying though so I have to take it out.

[ChoclateBetta]

Onion plants.