How reliable are large campaigns?

I have built quite a large campaign that is triggered from a long questionnaire created from Gravity Forms in WordPress. I broke this campaign into 6-8 smaller campaigns that are triggered from the main campaign which terminate with the contact receiving an email that their questionnaire results are available.

Everything seems to be working ok but I am concerned about the reliability of such a complex campaign. I recently was running a test and apparently the IS server became unavailable so it stopped with no notice (that I can find) in the middle of one of the sub-campaigns.

I am also using MyFusionHelper to perform calculations, and several times the results were not set correctly even though there was nothing wrong with the HTTP Post commands.

I am really concerned that we will have 50-100 people filling in the questionnaire and this will happen creating a MAJOR problem. Does anyone have any experience with this kind of campaign or are we using the wrong tool? We are getting ready to go into Beta and I want to make sure it isn’t too much to expect that this platform can handle the job.