While my wife is fine with me being MTF, she wants four kids, specifically with me. I was wondering and I did some research and storing... well sperm... does anyone know much about this. I already know I can't wait the seven or eight years for her to have three more kids.

I banked sperm, which I shall shortly be starting to withdraw (in monthly cycles) in the next week or so since my wife and I plan to have another baby now.  (The first baby was conceived au natural: now impossible due to HRT.)

Freezing sperm was a bizarre experience: a big open lab with women in white lab coats who directed to a room to do the deed.  The room was like a hospital room, but full of pornography (magazines and videos).  Upon finishing, the receptacle was taken away and that was that.  A fairly painless experience, and the staff were completely professional.

The only slight pain is that I froze sperm while we lived in Boston, but now we've moved to SoCal, so have to get it shipped over with every withdrawal (for not cheap).  It's a weird thought to think that part of me is in status a few thousand miles away, waiting to be woken up.

Do they charge to store it? And honestly I don't... do the deed myself, can my wife help me?

I'm not sure about point two but yes, these are commercial companies, they charge. You can Google places in whatever place you are for places and enquire about fees.

I think that the only people allowed to assist is Rosy Palm and her five daughters

I'll look into local companies then. And, while I'm incredibly uncomfortable with Rosy Palm and her daughters I guess I can live with that :/

My wife and I want at least one more child in addition to our 2 lovely daughters that we already have...  I have only come out to her in a few months ago and while she is completely supportive of me in anything that I do, she still is very unsure if our relationship will be able to continue as a marriage following any transition I decide to undergo.  That said I have done research...

I've read about some trans-women who have found that going off HRT for ~6-9 months results in fertility again (assuming no surgery has been done down there).  There is no way of truly knowing if things will start working again, but HRT doesn't necessarily kill it off forever.
http://www.milkjunkies.net/2013/05/trans-women-and-breastfeeding-personal.html (I was in a odd place mentally where the idea of helping out with the breastfeeding intrigued me, and while possible, I think the timeline of changes that would have to happen would be far too rapid for either of us)

Sperm banking is your other option.  My understanding is you pay to deposit, and they mix everything up with some antifreeze then cool it down way sub-zero.  There are some companies that are now offering at home deposit kits where you can collect and store deposits over a week or so of time and then send the kit in and they will set it up for long term storage.  You then are charged a yearly fee for holding your deposit.  When you want to make a withdrawal, they have to perform a separation to get the antifreeze out and heat everything up after which you have some choices about how you want to go about fertilization.  You can either pay a lot for in-vitro, or take your changes on the old fashioned method of introducing sperm to egg when she is ovulating.  The freezing process does result in ~50% loss in sperm count so the old fashioned method may not work all that well.

Just curious, what is the timeline of you having come out to her and her wishes to have 4 children?  Make sure that there isn't some level of her attempting to delay even subconsciously your transition in this request.  Having children is wonderful, but sometimes it is wielded as a ineffective tool to help cement a relationship that may be more rocky then it seems on the surface.

We've been married for a year now, I told her about 6 or 7 months before are wedding. However she didn't exactly get it then, but she's always known I was feminine. I made it clear not so long ago, but she already knew.

hehe, and after I typed that I received word from my wife that the third one may be on the way!  So excited!  No clue how all this will fit in with my exploration of gender though.

As for your situation, there are plenty of options and the final consideration comes to the two of you having very open discussions (possibly including a therapist) about how to proceed.  Neither of you should end up feeling rushed or delayed and that requires very clear, open and honest lines of communication.  Also, you have to ask yourself many questions on the topic of having children.  How many do you want?  How soon do you want to get started?...

Overall, I see a rather big adventure in your future ;-p

Thanks and congrats we'll probably see a therapist soon