hi my3fish,
I'll try and answer all your questions as simply as possible. Firstly the female looks like a wagtail. They are generally red/orange with solid black tail and dorsal fin.
It's difficult to tell from your picture if she's definitely pregnant but if she's been with a male recently then you can pretty much guess that she is. In terms of how far along she may be, again it's hard to say. There are signals to look for when the birth is imminant though.
Firstly if you look at her from the side and her belly is flat along the bottom she's getting very close. This is known as 'squaring off'. In simple terms she will take on an almost square shape.
Next you need to look at her anal fin area. When she's ready to drop it will start to open up. It will look swollen and it may look like she has a little tube sticking out of her bottom. This is the birthing tube and will close again after she's had all her fry.
With regards to fry - about 20 fry is about normal for my platies but there may be more or less. Be aware she will try to eat them - so will the other tank mates.
You can try putting her in a seperate tank (if you have one) or a breeding trap if you wish but if you decide to try this method be aware she may become stressed and abort her pregnancy. It's best to get her in there once she's started birthing so she's in there for only a short period.
Another option is to plant your tank heavily giving fry places to hide and just leave her to it.
Alternatively you may catch her in the act and then you can net out the fry as they are being born.
Regarding your male. He looks like a mixture of breeds of platies. Sometimes you get them in the strangest of colours - depending on what mum and dad were. I'd take a guess at some sunset in him and maybe some wagtail.
And also, Kitykat is right. You will need at least one more female - possibly two if the male is especially insistant.
I hope that helps answer some of your questions. Good luck with it all
Akasha