My '05 ST has the 2.3 Duratec, which I have read is very reliable, and it certainly has lots of very useable torque. Perhaps a ZX3 or ZX5 with the 2.3 and a 5 speed would be similarly quick and responsive, without the onus of higher maintenance (and insurance) costs. Another thing to consider is that Ford no longer fully supports the SVT with replacement parts, so you may be reduced to haunting salvage yards, or worse, ebay.de or ebay.co.uk, when Tousley can no longer get spares.
There is always the issue of the prior owner(s), and how well they maintained the car, and even if they scrupulously adhered to the factory maintenance schedule, they may have had their oil changes done, as I did once, by a shop that didn't realize the difference between an SVT, and a regular Ztec, and used the wrong weight oil!
Remember too, that two kids can require lots of time, and money. I speak from experience on that score.
All of this is simply to give you information on which to make your own, informed choices, not to discourage you from getting yourself a fun daily driver.
BTW, that $200 figure for the t-belt replacement is DIY, which, as you may have read, is a very finicky procedure. I would budget $600 to $800 to have a competent mechanic do the job.