I regularly work with oncology patients at a local hospital.
With the pedicure I use the Belava foot bath in which I use disposable liners. This means each client has a new and clean liner so no cross contamination.
I also use wooden cuticle sticks as again these can be discarded after use.
I do however use toe nails clippers if necessary but I soak all of my tools in barbicide.
I would suggest that you do not use a hard skin file on the heels, the skin is ultra sensitive so this is a no no. With regard to exfoliating I usually use exfoliating gloves, again these aren't to harsh and again one use per client.
With regard to massage I do do a very light massage, just enough to ensure the product has been absorbed.
If the nails are in an ok condition I paint them too.
All I would say is be prepared to adapt your treatments to a particular client and their needs, ask them about themselves and what they want. Just use your common sense if you have any reservations don't do it.
I don't have any experience doing nail extensions however I do manicures.
Nails can be in all sorts of conditions so again talk to your client.
I hope this helps.