#Japt, 50 40 34 28 bytes

V²o ®s1+Ul)£UgXnH)¯X¦0}Ãâ ¯V

Input is "string", number of items. Output is sorted by length, then reverse alphabet order. Test it online!

How it works

V²  o ®   s1+Ul)£  UgXnH)¯  X¦ 0}Ã â ¯  V
Vp2 o mZ{Zs1+Ul)mX{UgXnH)s0,X!=0}} â s0,V

Vp2 o      // Create the range [0..V²).
mZ{     }  // Map each item Z in this range to:
Zs1+Ul)    //  Take the base-(1+U.length) representation of Z.
mX{     }  //  Map each char X in this to:
XnH        //   Parse X as a base-32 number.
Ug   )     //   Take the char at index -^ in U.
s0,X!=0    //   If X is 0, slice it to an empty string.
â          // Uniquify the result.
s0,V       // Slice to the first V items.

This version takes a while if you want to do any more than 100 items. If you want a faster version, try this 32-byte one:

V*2 o ms1+Ul)f@!Xf'0î£UgXnH}ïV

Japt, 50 40 34 28 bytes

V²o ®s1+Ul)£UgXnH)¯X¦0}Ãâ ¯V

Input is "string", number of items. Output is sorted by length, then reverse alphabet order. Test it online!

How it works

V²  o ®   s1+Ul)£  UgXnH)¯  X¦ 0}Ã â ¯  V
Vp2 o mZ{Zs1+Ul)mX{UgXnH)s0,X!=0}} â s0,V

Vp2 o      // Create the range [0..V²).
mZ{     }  // Map each item Z in this range to:
Zs1+Ul)    //  Take the base-(1+U.length) representation of Z.
mX{     }  //  Map each char X in this to:
XnH        //   Parse X as a base-32 number.
Ug   )     //   Take the char at index -^ in U.
s0,X!=0    //   If X is 0, slice it to an empty string.
â          // Uniquify the result.
s0,V       // Slice to the first V items.

This version takes a while if you want to do any more than 100 items. If you want a faster version, try this 32-byte one:

V*2 o ms1+Ul)f@!Xf'0î£UgXnH}ïV

#Japt, 50 40 34 28 bytes

V²o ®s1+Ul)£UgXnH)¯X¦0}Ãâ ¯V

Input is "string", number of items. Output is sorted by length, then reverse alphabet order. Test it online!

How it works

V²  o ®   s1+Ul)£  UgXnH)¯  X¦ 0}Ã â ¯  V
Vp2 o mZ{Zs1+Ul)mX{UgXnH)s0,X!=0}} â s0,V

Vp2 o      // Create the range [0..V²).
mZ{     }  // Map each item Z in this range to:
Zs1+Ul)    //  Take the base-(1+U.length) representation of Z.
mX{     }  //  Map each char X in this to:
XnH        //   Parse X as a base-32 number.
Ug   )     //   Take the char at index -^ in U.
s0,X!=0    //   If X is 0, slice it to an empty string.
â          // Uniquify the result.
s0,V       // Slice to the first V items.

#Japt, 50 40 34 28 bytes

V²o ®s1+Ul)£UgXnH)¯X¦0}Ãâ ¯V

Input is "string", number of items. Output is sorted by length, then reverse alphabet order. Test it online!

How it works

V²  o ®   s1+Ul)£  UgXnH)¯  X¦ 0}Ã â ¯  V
Vp2 o mZ{Zs1+Ul)mX{UgXnH)s0,X!=0}} â s0,V

Vp2 o      // Create the range [0..V²).
mZ{     }  // Map each item Z in this range to:
Zs1+Ul)    //  Take the base-(1+U.length) representation of Z.
mX{     }  //  Map each char X in this to:
XnH        //   Parse X as a base-32 number.
Ug   )     //   Take the char at index -^ in U.
s0,X!=0    //   If X is 0, slice it to an empty string.
â          // Uniquify the result.
s0,V       // Slice to the first V items.

This version takes a while if you want to do any more than 100 items. If you want a faster version, try this 32-byte one:

V*2 o ms1+Ul)f@!Xf'0î£UgXnH}ïV

#Japt, 50 40 34 28 bytes

V²o ®s1+Ul)£UgXnH)¯X¦0}Ãâ ¯V

Input is "string", number of items. Output is sorted by length, then reverse alphabet order. Test it online!

#Japt, 50 40 34 28 bytes

V²o ®s1+Ul)£UgXnH)¯X¦0}Ãâ ¯V

Input is "string", number of items. Output is sorted by length, then reverse alphabet order. Test it online!

How it works

V²  o ®   s1+Ul)£  UgXnH)¯  X¦ 0}Ã â ¯  V
Vp2 o mZ{Zs1+Ul)mX{UgXnH)s0,X!=0}} â s0,V

Vp2 o      // Create the range [0..V²).
mZ{     }  // Map each item Z in this range to:
Zs1+Ul)    //  Take the base-(1+U.length) representation of Z.
mX{     }  //  Map each char X in this to:
XnH        //   Parse X as a base-32 number.
Ug   )     //   Take the char at index -^ in U.
s0,X!=0    //   If X is 0, slice it to an empty string.
â          // Uniquify the result.
s0,V       // Slice to the first V items.