Dear Samina,
1) The word abhyanga is used to denote application of oil.
Nowadays it is used to denote massage done by using oil.
There are various substances which can be used for massage and
ayurveda names them accordingly.
However in general terms abhyanga is the form of general massage
suggested as a part of daily regimen according to ayurveda.
As such there are no contra-indications for abhyanga as long as it is
used as part of daily regimen.

2) The benefits of abhyanga as mentioned in the texts are :-
a) Removes fatigue
b) Cals vata
c) Improves eyesight
d) strenghtens the body
e) Induces longevity
f) Induces sound sleep
g) Strenghtens the skin and improves skin colour and texture.
h) Aids resistance to disharmony and disease.
i) Soothes ailments caused by Vata and Kapha.

3) For general purpose the following oils can be used for a
particular dosha :-
a) For vata - sesame oil
b) For Pitta - coconut oil
c) For Kapha - Mustard oil
Besides a number of other oils either alone or as a combination
prepared from various herbs are used.

4) For general massage (abhyang) many factors are considered. A few
of them are :-

a) Prakriti - Constitution i.e Vata, Pitta, Kapha
b) Age
c) Ritu - season
d) Occupation
e) Climate (this is different from ritu as the climate during
summer in India will be different from climate during
summer in UK)

If you want to refer to good book on ayurvedic massage you can refer
to "Ayurvedic Massage" by Harish Johari.
The ISBN No. is 0-89281-489-6.

Cybervaidya.