How important is mars in figuring out compatibility between two people?

If Mars squares Venus there is stress in the relationship however if it's trine or in conjuction or sextile it's in flow, if it's inconjunct you also will not see eye to eye as well as opposition will create tension.

It's how your Mars to his Venus is that is more important than how your Venus's relate get it? Everyone has an inner male or female so you need to see how integrated that is,

If his Venus is in Scorpio and your Mars is in Virgo that is a good match because they are both female signs and are sextile each other. If his Mars is in Sagittarius that is also Sextile and that is Male for his Mars and Female for yours so its a good match. Two Capricorns should get along with this energy and as long as you don't get pushy with your Leo Moon, you will be ok as it is inconjunc the Libra Moon of his which is in exaltation. I don't know your aspects so this is a lot of guess work

the questioner despite having knowledge on the subject,
instead giving full details of birth date etc,
expecting guess work
is obviously
beating around the bush,
as the positions, aspects, placements etc of other planets
do say about the natal chart , besides with the help of divisional charts, if need be ,
pl, . , give details of birth (s),
and compare the answers , with the knowlede gained by the questioner,
to lead comfortable life,
good luck,

It isn't.

The only way that you will ever find out whether you can have a good relationship with someone is to spend lots of time with them. Don’t ask ‘astrologers’, these people know nothing at all! They don’t know you, your hopes, dreams, fears or aspirations. They are simply money grabbing parasites who see you not as a person, but as nothing other than a business opportunity. Never allow yourself to be fooled by these people.