How to use counting in text
Is it ok to write like that:

There are two things I want to tell about: First, I like Italki and the site's interface. Second, I find the community quite helpful.

Question

How to use counting in text
Is it ok to write like that:

There are two things I want to tell about: First, I like Italki and the site's interface. Second, I find the community quite helpful.

Answer

Your text is correct. You can say 'first' or 'firstly' etc.

Here is a great article about enumeration: http://grammarist.com/usage/firstly-secondly-thirdly/
And an article about usage: http://www.oxforddictionaries.com/words/why-do-we-use-first-second-and-not-firstly-secondly

Hope this helps

Answer

'Firstly' and 'secondly' would be better.

Answer

I think I decided so too))

Answer

Sure.  Perfect.
Some may argue that you should use firstly, secondly... but first or firstly  are equivalent and I would apply 'the law of parsimony' to use the simpler form - unless there are poetic or rhyme or rhythm reasons.