Ideas I'm considering:
-more guest blog posts (SPECIFIC suggestions welcome!)
-webinars (I've done a webinar with the Project Management Institute in Nov 2014 and have another in the works; who else can I do a webinar with?)
Website Founded: June 2014
Current Email Subscribers (with Aweber): 141
Landing Page For Email List: http://projectmanagementhacks.com/SponsorReport
Guest Blog Posts published in 2014: over 50 (full listing here: http://projectmanagementhacks.com/portfolio/
Seems like you're headed in the right direction, especially with the webinars and the guest blogging - these are a great way to increase the interest to your service.
Also, 900 subscribers by May sounds totally realistic.
However, the website definitely needs a lot of work. It looks like a general blog, nothing too professional to convey trust and authority. No additional pages for your services, it's hard to get in touch with you, the only lead form is the Hello Bar on the top (that is a bit too large).
The landing page and the exit intent popup are also really bad - you'll have to work on the design aspects or use plugins such as OptinMonster for optins and Unbounce/LeadPages for landing pages.
No related posts, no way to convince a user to stay after a post is done.
The list is long, I can share a few other things as well and help you with the design concept and measuring your leads if you're interested.
You are on the right track, and the numerous guest blog posts are a good start. Your landing page definitely needs work, though - both in terms of visual design and conversion optimization.
One great way to drive more traffic back to your own site from guest blog posts (since that one link in your bio won't get many clicks) is to create an offer *specifically* for the readers of that particular site. Take for example your guest post on letsgrowleaders.com. Spend a couple hours bundling up some content (could be a PDF download, a template, a worksheet, etc. - feel free to get creative here) that caters specifically to that audience ("3 Project Management Templates for Leaders"), and then embed that offer at the bottom of your guest post. Be sure to get permission to include a call-to-action for that offer from the folks you're blogging for, of course, but crafting a unique offer for *their* audience will often win their approval.
I'd also recommend building out a module to collect email addresses directly within the post in addition to linking to your own landing page for the content -- it should help you increase your conversion rate & collect more emails.
Hellobar is actually a good option but given your skills probably would be best if you use something like http://convertkit.com/
I'm with Mario on considering a big of a redesign to convey a little more trust and authority. Might seem like a big investment now but it's totally worth it.
In terms of growth though, free reports (PDF downloads), and webinars are a great growth strategy.
In 2003 for example we launched this site with 5 PDF reports, and 3 audio interviews (case studies): http://www.agentpress.com. We got 3,000 subscribers in about 1.5 months.
Try pop-up domination, design a good opt-in and offer the free report as an incentive.