There is no "proper way" BECAUSE Raspbian DOES NOT use Debian networking, although it is still possible to use this if desired.
dhcpcd as its default network manager. See How to set up networking/WiFi for detail.
Why do you WANT to "interface up/down" -
dhcpcd automatically manages network interfaces, and does an excellent job?
You can write hooks which are invoked by network events - see
man 8 dhcpcd-run-hooks (There are a number of included hooks e.g.
PS Using a Pi as a WiFi repeater seems a poor idea, due to the restricted network throughput - a dedicated repeater would be cheaper and perform better.
Incidentally you can still use
/etc/network/interfaces if you configure
dhcpcd to NOT manage an interface (discussed in linked answer).
Stretch networking is the same as
The earlier Foundation implementation of
Wheezy) omitted the
10-wpa_supplicant hook, requiring a kludge in
/etc/network/interfaces to support WiFi. (In fact I installed
10-wpa_supplicant in my
Stretch introduced predictable network interface names which are incompatible with the kludged
/etc/network/interfaces so the
10-wpa_supplicant hook was included. (For some incomprehensible reason the Foundation later decided to disable predictable network interface names.)
If you want
Stretch networking to work the same as
Jessie all you have to do is delete
10-wpa_supplicant and restore the kludged
/etc/network/interfaces. This will, of cause, suffer from the limitations of