If it's any help, i run two formations of HST depending on space available (using the old Hornby power cars but the principle is the same).
A full length rake has between the power cars: TGS + TS + TS + TS + TRSB (or whatever!) + TF + TF giving a Western Region formation of 2 power cars plus seven trailers.
A short rake (for running on my own layout) has the two power cars (of course!) plus TGS + TS + TS + TRSB + TF or TGS + TS + TRSB + TF + TF, depending on which takes my fancy at the time.
My trailers are all older Lima and Joueff (repainted), but Hornby have made blue and grey trailers in the past so you may be able to pick these up second-hand.
If you can't fit a two + five formation, drop one coach to do as you suggested in your post, ie TGS + TS + TRSB + TF.
Note: I've forgotten what the correct designation for the Lima restuarant/buffet coach is so I've used TRSB here but it could easily be a TRUK or TRUB, or classified versions of those - I'll have to check this later.
A full length rake has between the power cars: TGS + TS + TS + TS + TRSB (or whatever!) + TF + TF giving a Western Region formation of 2 power cars plus seven trailers.
A short rake (for running on my own layout) has the two power cars (of course!) plus TGS + TS + TS + TRSB + TF or TGS + TS + TRSB + TF + TF, depending on which takes my fancy at the time.
My trailers are all older Lima and Joueff (repainted), but Hornby have made blue and grey trailers in the past so you may be able to pick these up second-hand.
If you can't fit a two + five formation, drop one coach to do as you suggested in your post, ie TGS + TS + TRSB + TF.
Note: I've forgotten what the correct designation for the Lima restuarant/buffet coach is so I've used TRSB here but it could easily be a TRUK or TRUB, or classified versions of those - I'll have to check this later.