That window is entirely covered by a rock solid core. The infield is set with the exception of just one position at third, the rotation has three solid to great starters signed long term, I hate the way the outfield is setup but it is mostly under control for a couple more years, and the bullpen...well, the Jays are pretty good at finding value relievers. For the most part, if the season were to end today, there are few enough holes that they could all be covered by free agent signings, and there is lot of money coming off the books in a few years.
As for improvements the Jays need right now, the only way they could really improve on multiple positions is to trade for players that are elite or better, each of which would be highly costly in their own right. That strategy is unfeasible and would need to be massively impactful at too many positions to make a big enough difference, so their best best is to target significant major additions at their weakest positions, and their best capital in that regard is prospects. Can they afford to do so?
Absolutely. Almost all of the core pieces are young to very young players who will be hitting their contracts before their 30s, windows that overlap with many of the top prospects in the Jays systems, none of which look like slams dunks (Groshans is cool but still no power, Martinez whiffs more than a fan, Horwitz is a 1B and we don't need more of those, etc). The starters are older but by the time they go bad you'll have Tiedman and Berreria ready, and this is buoyed by having Castillo (even better if Pearson finds his groove and they manage to fix Kikuchi). This 3 to 5 year contention window is plenty of time to rebuild the farm system, and there are still a whole bunch of interesting prospects in the Jays system that are too young to attract any interest. And considering how they drafted, it looks like they're planning entirely on high payoff gambles that could potentially restock the system.
So, yes, NOW is the time. Now they can afford to unload. There's only like a couple really important prospects worth keeping and the rest are low enough on the list other teams might miss them. And this draft looks like it will bring in a bunch of intriguing names. So, yeah, I say GO FOR IT.