PostgreSql Doubt

Hello,

I have a data source for example in file format(xml,csv ..etc) , i want to
use postgresql engine to query select,update,insert using foreign data
wrappers(fdw).

question1 --- > is it possible to prepare our own fdw ?.
question2 -----> is it possible to seperate postgresql engine and use it on
a data source where i will write fdw to connect the postgresql engine and
data source ?.
question3 -----> In fdw , we need to provide schema of the file , suppose i
will get schema of the file in a varaible and how can we use this variable
and directly create a link between datasource and postgresql engine ?.

question4 -----> is this fdw(foreign data wrapper) good to use in
postgresql ,if so did postgresql prepaired any api kind of fdw officially ?

Thanks
aluka