Stocking my future 20 gallon long^^

Question
Hi, i plan to get a 20 gallon long tank in the future.  I know about fishless cycling for the beneficial bacteria so thats good.  I will be putting sand (play sand to be exact) in the tank if that affects anything on my stocking/compality (sp?) levels.

The fish i want to have in my 20 gallons are:
1 Banded Gourami (Colisa Fasciata) as a "center-piece"
4 Three-stripe/line corydoras (corydoras trilineatus) feisty little guys xD
3 Red Wag Swordtail (Xiphophorus helleri) 1 male:2 females
7 Neon Tetras (Paracheirodon innesi) what a classic :D

I thought of this stocking because i read in about 5 aquarium books that to find the total stocking your tank can hold, (with reasonably small fish, no oscars using this rule!) find the surface area and divide by 12, the number is now many inches of fish you can have.  

My 20 gallon long is 30x12 so divided by 12 would be 30 inches of fish.  so that would be, in respect to the order up there^, 4+(4*2)+(3*3)+(7*1.25)=29.75 inches of fish. I dont even know if i have their lengths correct though.  

First off, are all these fish compatible with each other? I chose them because gourami usually stays at the top to breath, swordtails in the middle, neon for schooling, and corydoras for bottom.  If they are compatible, will this stock work or will i have to cut down fish o.0

I know that my swordtail will have babies but i am willing to take as much as i can out if i dont get them in my breeding box in time.  I have spare tanks (10 gallons) that i can keep them in and fish stores/friends that probably will take them.

Also, i am always up to taking suggestions on other ways to stock this tank^^

about tank maintanance, i will do about 50% water changes once per week or change as much as it takes so that nitrate doesnt pass 40ppm in a week(i will do this by testing and testing and testing D:) I will have some plants too that will help me removed nitrates.  

Tank decor is going to be a 7 inch ceramic bubble stick (if it can count as decor xD), a terracotta clay pot, and a huge 36' bamboo thing which gives plenty cover horizontally and vertically.

Sorry if im rambling a lot in some places, im just trying to give as much info as possible ._.

Thank you very much^^ hope to hear back as soon as possible

Answer
Hi Harry,
Wow! I must give you a million cheers for doing your research before stocking your tank beforehand! Very few people go to so much trouble to insure their tank setup is perfect. I'm impressed!

You seem to have everything figured out just fine. I think your stocking level is just about perfect, and you will have a nice variety of fish in your tank without it being overstocked. Your maintenance schedule is excellent also.

There's not much more I can add to this since you have everything so wonderfully worked out and well-researched beforehand.

Best of luck with your new aquarium!
Karen~