Adding a second bathroom

ok, I have been reading up and researching about the possiblies of adding in a second bathroom, (sink, toilet) in my basement.
After reading about venting issues and exit issues I am still a bit concerned about adding the bathroom.
I am hoping that someone can give me an idea what I can do to resolve my issues.
From what I have been reading, any "P" trap needs a vent.
After, looking at my main stack I noticed that my vent is located on the left hand side of the stack and is last in the line of supplys before my main continues the rest of the way down and out of the house and all the supplys, from the kitchen, tub, toilet and bathroom sink are located on the right hand of the stack. From there my 4" main runs down along my foundation and out my foundation at the first row of block. On the out side of the house in my front lawn there is a 4" main vent that sicks up about a foot above ground with a cap that alows air into the main.
Here is where my questions start.
If i was to tie in to the 4" main after the stack down stream, should I still run a vent for both the new toilet and sink back to the main vent stack or would the 4" main vent sufice?
I have attached a photo of the 4" main vent in my front lawn.

I took better photos of the main stack yesterday and the vent pipe in my front lawn. As soon as I get them develped I will post the new photos. Hopefully some one has a good idea

Are we to understand that your main drain exits through the wall?

If that is the case, you will need an ejector pump for your fixtures.

Both sink and toilet need to be vented. The distance from the flange to the vent must be 5 feet or less. The sink (vent) can be tied in to the same vent for the toilet at 42 inches above the flood rim of the bowl at least. Also there can be no drainage of other fixtures from above for this basement bath vent except to tie in at least 42 inches above Floodrim of those highest fixtures.

Be sure to consult local codes for the final say.

P.S. The rule is any fixture (not p-trap) needs to be vented. There are various ways to vent different fixtures. Toilets do not have p-traps they have a integral trap which serves the same purpose.