~のは…ぐらいのものだ => only (emphasis) N1
Limit
いつかの ... => Previously N4
Time
くらいの => Approximate~ N3
Emphasis on degree
というのは => because N2
…ばあいをのぞいて => Except for N2
Exception
…からいいようなものの => It’s a good thing that… this time… N1
Criticize
…の…ないの => thinking whether or not to do something... N2
Position, perspective
... ないものは ...ない => is not entirely impossible N3
Ability
... というのは => It means... N3
Explain
どのくらい => how long N5
…くらいの…しか…ない => Only… at low level N2
Limit, limit
ぐらいのものだ => Only A N1
(Not)only , (Not) even