i have a similar strategy to yours. BlatentAnarchy taught me it (he's number 1 in the PS3 zombie leaderboards)
rounds 1-5 (or first dog round): stay at the mainframe and do the let em in n shoot trick.
rounds 6-9: when the first horde of dogs come or your at the end of round 5, open the to doors to the Thompson room. stay there for a while with 1 person covering the windows and the other 3 near the double barrelled shotgun. (don't forget to buy a thompson)
rounds 9-15 (at the latest): at the end of round 9 keep a crawler and get all the guns out the box. you should've spent all your money on guns (should've had around 10k each). now hold off at the courtyard and make sure the door behind you is CLOSED. then at any round you can link up the teleporters and such.
round 15-23: once you've linked up the teleporters (should be done by round 15) open the door to the catwalk (behind the courtyard) and have one person in the tunnel covering the window, one at the balcont covering that window, one at the quick revive window and one person who stays in the courtyard (if your gonna stay in the courtyard you WILL need juggernog and speed cola). the person in the courtyard must be skilled though. perks and good weapons won't save you.
rounds 23-30: it is reccomended now that the people at the windows move to the catwalk because the zombies seem to be MUCH stronger in the mid 20's. the person running around in the courtyard can stay there if he wants be he will have much more trouble keeping the zombies back. if the person in the courtyard gets pushed back then the zombies from the balcony and quick revive will go to him and he will be trapped.
30-35: now even BlatentAnarchy has to pull back. no matter how good you are you cannot stay in the courtyard by yourself no matter how good you are. you WILL get overwhelmed. so now everyone should be on the catwalk (i prefer to stay in the quick revive by myself because the zombies from the courtyard go straight past me so i only have to worry about the window and maybe a sneaky dog.
35- : well i hope you've kept your money because now its time to start teleporting. the zombies are really hard to kill now. if you were on the catwalk you will get EASILY overrun. but dont just teleport. shoot then aswell for more points and wait till the zombies are in the teleporter too. then they will get killed. once your at these round it takes about half an hour per round! so if you wanna get far you better put some time and effort in!
i would explain what i have experienced in the 40's but i cant. my highest round was 40 before we lost connection
don't belive me? link: [ame=
https://www.youtube.com/watch?v=seF9QEhWHzQ]YouTube - Nazi Zombies Level 40 In Der Riese With Voice Strategy & Subtitles[/ame]
this has turned into a essay hasn't it 0_o