Publishing Bundles on Kindle

Hi. Just a question... I'm currently working on a short story for Kindle. I already have a 90,000 word novel on there (the short story is 15,000 words) which I've managed to sell around 40 copies of in the last couple of weeks now off the back of free days (it sat there a month with only 20 sales to friends). But as I learnt on here when I posted last time (and thanks for all your advice), you really have to have another title to offer to cash in with free days. 13,000 downloads, I'm kicking myself now!

Anyway, this short story will be part of a trilogy. I should finish up and hit publish this weekend (I was planning to, anyway). But I've been told that with short stories that are part of a series, it's better to wait and bring them all out together rather than dripfeed them. In an ideal world, that's what I'd do, but whilst this one is easy to write, the other two will require a lot of research, and rather than taking a couple of weeks to produce, it'll probably be more like a month apiece. Then you've got the 60 day waiting period to collect funds from Amazon... I could do with the cash asap. The short stories will be the same genre as my novel, but not the same niche (the niche of the short stories is very specific whereas the novel was pretty wide).

I know it makes sense to wait from a longterm point of view, but would it be hugely detrimental to publish the first one now? I'd just thought free days would help boost sales of the novel (they've dropped off a cliff again in the past few days) and vice versa. What do you guys think?