When can I convert my coins from one asset to another? When will this platform be launched? And what is required for registration on your exchange?
Conversions will be possible once the Wallet and Treasury applications are launched in Q1 2019. No registration on the Exchange is necessary. See the WP for more details

Excellent, it is a good speed of development for your system. I think I will use your features immediately after launch. Will the test phase be closed to external participants?
I think that with the high speed of development we may not get access to the alpha version of the products. This is not necessary, but maybe the team will be able to show us a brief overview of the interface?