usb modem e3372
if your e3372 is working fine with the tp-link, it might also work with the hAP ac lite.
as Pukkita said, you can use your hAP to connect to the wifi of the wifi and use the 5GHz radio to create another network.
the other solution would be to stick the e3372 into the hAP ac lite's USB port. now this is where the story gets confusing.
depending on the firmware version you have in the modem, it can be detected as LTE device or as ppp-compatibility device.
the latter one is a more cumbersome situation (firmware starts with 21.xxx): your dl speed will be limited at 20-25Mbps. but you will have "direct" connectivity to the mobile carrier's network, because your router will receive the IP from the mobile network. the modem will be shown as a port in "/ports" and will be used by the ppp-client, where you need to set up some things, like APN name, authentication if your carrier requires it, which channel to be used with the modem, etc.
so something like this (the stars denote where you will have ip address)
[mobile network*]- - - - -[e3372 as modem]- - -[*hap ac lite*]--- your network
if your modem has the huawei "hilite" fw, it will be running at full speed, but it will act as a router. (firmware starts with 22.xxx)
[mobile network*]- - - - -[*e3372 as router*]- - -[*hap ac lite*]--- your network
in this scenario the e3372 will establish the connection and receive IP from the mobile network. it also has a subnet (usually 192.168.1.0/24) configured on the "USB" side, similarly to USB tethering. your hAP ac lite will need to use DHCP on the device created in "/interface lte", and will receive something like 192.168.1.100, or similar. you shall avoid using the same net in your local network, otherwise it will not work properly.
with this setup your mikrotik can not be accessed from the outside, as the dongle in router-mode will do NAT, and you cannot really configure on the dongle anyway.
in this case you do not have no chance to modify any mobile network related settings from routeros, at least not with 6.40. but there is a web interface running on the dongle, so by typing 192.168.1.1 in your browser - when you are connected to the router and the modem is plugged in & active - you will see the settings page of the dongle.
as far as i know the e3372 can not work in transparent LTE mode with routeros 6.40 and prior. but in terms of speed, the "hilite" stuff is quite nice. later releases will probably have better support.