I know there are 3rd party extensions for this but i prefer the default OPC and would just like to reduce the number of steps.
Ultimately i would like to combine the Shipping Address and Shipping Method into one step and if possible do the same with the Payment Method and Order Review steps.
Any help on how i can achieve this would be greatly appreciated.
Its worth mentioning a very similiar question was asked here CE 1.9.2 - Onepage checkout - merge shipping address and method into one step although when i followed the instructions i was unable to proceed past the billing step so i'm assuming something is missing.
This sounds like a slippery slope, but if you'd like to achieve it the files for this are located in
app/design/frontend/base/default/template/checkout/onepage/progress and should be copied to AT LEAST a custom "package" for your use, instead of overwriting the original core files.
From here, you should be able to combine the information in these files to a certain degree. Mind that you will also probably need to update the file
../template/checkout/onepage.phtml to remove extra steps that would now be empty/duplicate.
There may be other
.xml or even
.phtml files to update with this customization as well but I'm not sure which ones as I've never attempted the change you desire.
I would caution you with this: shipping is not always duplicate to billing and it's easy for the customer to select "use billing for shipping" during checkout. There's also some calculations that happen between these steps to ensure the right options are made available.
I would expect a heavy amount of customization to make this happen - but if it works, you'll have a working "extension" to market to others who want this option as well.