Spouasal maintenance

Please help

I need to get an understanding of what my spousal maintenance liabilty might be as it looks like we are now seperating and I have no idea of what I will have to live on...

#We have been married for 5.5 years.
#Age: Me 45 Wife 36
#We have one child age 5
#I will have my child for overnight stays for between 70 - 100 nights per year
#My Basic salary is £67K with approx £7K extra standby payment and I have company car and company pension.
#My Wife earns approx £7.5 -8.5K PA working part time (she has been working for approx 6 months of our marriage)
#We currently share a mortgaged property value £280K with approx £120K outstanding on the Mortgage, I met all mortgage payments.
# I have a second property that I lived in before we met and I am now letting, the value of this is approx £145K and has £130K outstanding on the mortgage, although it is let the rent only covers the mortgage so there is no income from it, infact it is an expense of approx £30 Per month

Me
# I have shares vlaue less than £500
# I have an ISA value ~7K
# I am currently paying child support for a child from a previous relationship of approx £360 Per month

Wife
# My wife has a car Value approx £9k
# She has an ISA £7k
# she has 2 other children from her previous relationship that she gets ~£576 per month
# She has a personal pension but I have no idea of the value
# I would guess that she has approx £5k in other savings

Current outgoings for home we share per month
#Mortgage £760 pm
# All other bills ~£390
# Shopping ~£1100 - £1200 per month

Please can someone give me a good estimate of how much beyond child support I would need to pay.