You should definatly have more than 5mm movement.
Having very little feel to the pedal indicates it is not depressing the clutch plates.
This could be a sticking release arm, so try disconnecting the slave cylinder clevis and seeing how easy the arm is to move. It should be free to move, untill it makes contact with the release bearing. If it is tight, or near impossible to move by hand, then the release arm has seized (quite common)
Then the next thing I would do is bleed the clutch.
An "eazy-bleed" kit works wonders on the clutch!
Then see how much clutch arm movement you have. If still very small with no effort, then i would suspect the master cylinder.
If I were looking at this on my car I would just go straight for master cylinder and slave cylinder re-seal , followed by eazy-bleed to replace fluid and thoroughly bleed clutch (remember the pipes are long and go all over the place from front to back, so not as easy to bleed as normal clutch.
Although not a big issue. as the cylinder is angled slightly up, so I suspect some air remains in slave cylinder after normal bleeding, so I also bleed the slave cylinder a little special!
Note this is generally not necessary, but can improve a good clutch to a great clutch!
1 after normal bleeding is complete
2 Press clutch peddle down and hold down with a bit of wood or brick (or a spare wife)
3 Gently release the bleed nipple and allow clutch arm to move back under clutch force
4 by hand push arm further back, forcing the slave cylinder all the way in untill it can go in no further.
5 Close bleed nipple
6 remove wood, brick or wife from clutch peddle and allow peddle back up.
What this does is completely remove any air that might be trapped in the slave cylinder.
Once the hydraulics are 100% then look for other issues in the clutch.