Well; Kali is popular because of the cult of script kiddies that follows it.
But one for the vpn; once one has termux installed just do:
apt install openvpn vim
The built-in vpn client on most modern android releases is very good but if one wants to play with more linux based stuff then try ppp over ssh, or openvpn.
As for IDE on android, I’ve found that’s a week point one usually shored up by Termux and vim, or cloud9 ide depending on one’s screen size.