multiple WAN aggregation

hi there,
i live in an area where the ADSL speeds stinks, and the 4G is mediocre
so the goal that i am trying to achieve is to combine the speeds of multiple sources into 1 fast connection that gets spread around the house later

so here is the current setup:

the output (aggregated link) from the MikroTik switch/router will be attached to the main home router (amplifi)

now the question:
1- is my understanding about link aggregation/load balancing correct ?
2- what is the best mode to achieve it ?
3- what MikroTik appliance should i chose ?
4- any suggestions on how to improve the setup ?

with regards
ahmad