Practical for a civilian to build a space suit?

onomatomanic

I certainly agree with Ryan on one thing: If any one thing goes seriously wrong in a closed ecosystem, once the outside world has become uninhabitable, the results won't be like those of the man-made or natural disaster we are used to. The result will quite simply be that everybody dies.

Thus, building a flawed ecosystem isn't much of an improvement over not doing anything at all.

As a suggestion, if the reason for your insistence on the five-year time limit is that you don't want the setting to become too futuristic, you could instead set this in an alternate timeline in which the Black Hole was detected in 1970 and will arrive in 2020. That gives you the development timeframe which others consider more reasonable, and technology in areas not directly related to preparing for the catastrophe would still be more or less where it is today in this timeline. Probably less, in some case, because resources have been diverted.