How to speed up an insertion from a huge table with postgres?
.. a new table that contains all columns of all tables .. 


Really?  That's unlikely to be useful. 


  select .. from t1 join t2 join t3 join t4 ...


Without "on" clauses to tell postgres how to put the tables together, those 'join's will link every row in t1 to every row in t2 and then every row of that to every row in t3 and then every row of that to every row in t4 ...   

That's an awful lot of "rows". 

As always, build a select statement that returns the data that you want, then just add the "insert into" bit on the front of it. 

If your tables are all the same structure, I'd suspect you'll be better served by 'union [all]'s instead of 'join's but YMMV; we can't tell because you haven't given us the structure of your tables or your intended result.