1.Considering that the MiG-21 PF/MiG-21PFS, MiG-21PFM and MiG-21FL ,MiG-21 R, MiG-21 S/MiG-21M and MiG-21 SM/MiG-21MF,MiG-21 MT and MiG-21 SMT all used saddle tanks.. I believe thats more than few. But as you wish.
2.Isnt Skin Friction, Form considered a part of parasitic drag?? i.e the drag due to the object moving through the fluid?
3. Yes.. which is why the physical dimensions of the model lead to the fuel argument.
1. Yes they come under parasitic drag. Parasitic drag is sub divided into Form and Skin Friction. While Form drag deals with cross sectional area, skin friction deals with the friction between surface and the fluid. ( Cross sectional area will remain mostly the same but skin friction will increase.) (Parasitic drag will increase but due to SKin friction and not Form). Still I am kinda rusty on these definitions part so you may have to check it out for yourself.
2. Wait and See.