If I recall correctly from my rental time on the Imacon: the medium format holder can take a strip three x 6cm square exposures long but one will only be partially viewable. I think that a 6 x3 5mm strip will fit in the 35 mm strip holder and all will be viewable.
I have the Imacon 646. It came with four holders. The 4x5 holder holds one negative, the 60x70 holds one negative, and the 60x60 holds two negatives. The 35mm holder has the option of holding one vertical and one horizontal but I think you have to choose one orientation or the other.
In short, this particular model is very good for scanning one neg at a time but is no way a batch scanner (I am not even sure that Imacon makes a batch scanner attachment for this model??)
35mm mounted slide - holds 1 frame
35mm Batch mounted slide holder - holds 1 single frame in a magazine which can take up to 50 slides
35mm strips - holds up to 6 frames
120 - various different single frame holders or a 6x18 holder which will allow you to scan 3 frames of 66 in 1 go.