~ Is it really viable?
Distributed teams are very common. If you are startup is not having to deal with shipping/receiving or if onsite events are not critical; then there are plenty of proven examples where a remote team is viable.
~ Will it be harder to bounce ideas and be innovative?
As long as all stakeholders communicate regularly and a system like Slack or Discord is adopted, it shouldn't be.
~ Will this kill momentum?
Only time this might is around an actual product launch where timing is critical for success. Otherwise it shouldn't impact anything.
~ What are your immediate concerns?
My only concern would be that adoption is key. If you both are unfamiliar with or haven't adopted agile methods for remote work, I think there will be some growing pains. But if you both commit fully to the process and the project, being remote shouldn't slow you down.

There isn't a such a service per se. There are several methods we us to find bloggers but most are more manual. They are:

1) Via conferences like Affiliate Summit (largest affiliate conference in the US), Type-A Mom (one of the most active mom focused blog conferences), NMX (largest blog conference in the US), PubCon, AdTech, etc.
2) Via analytics tools like Salesforce Cloud (formerly Radian6) that allow queries/searches based on content created in social media
3) Identifying bloggers that are open to affiliate deals based on which ad networks, if any, they are already working with.
4) There are also still plenty of active forums: A4U, ABestWeb, and Affiliate Summit's own forum.

It depends on the following two questions:

1) How good is your in-house team at compliance and enforcement? Affiliate is very much still the Wild West. This means that there will always be some affiliates either stealing commissions from other affiliates in your program, doing things that may put your company in legal jeopardy with the Feds, or cannibalizing your other channels by stealing credit for sales they didn't drive thus impacting your ROAS.

2) How extensive is your network of potential affiliate contacts; and if it is not extensive, how compelling is your offer/brand/niche to affiliate partners?

If you have time and expertise for deal with compliance and if you feel you have a big enough pool of potential affiliate partners; then I would go with a paid established software like DirectTrack. If not, I would go with an affiliate network like ShareASale (mentioned by one of the other commenters) or ImpactRadius (which has a lot of flexibility).

Regardless, I would not go with an Open Source software solution unless your dev’s have time on their hands. Whatever you might save in network fees or software fees you will lose 2x in ongoing dev costs and opportunity costs.

So this model has been attempted before in various formats. As a direct comparison, 3-4 years back there was a company called WidgetBox. They were a startup. Successful in getting funding. Raised at least $8 million. Their changed up their model a few times but their most successful one was nearly identical to what you described. They went directly to various advertisers on a CPA basis and then guaranteed publishers a set CPM based on the agreed CPA with the merchants. Got as high as doing 500 million impressions a month. But they didn't appropriately account for fraud, had to back out on payouts, ended up nearly folding. They were able to pivot and be absorbed into Flite.

A less direct comparison of your scenario is very common. Many affiliates these days operate what is considered a sub-network (against the rules of most larger affiliate networks) or a super-affiliate program. Examples are the dozens of loyalty affiliates out there like Upromise who also have their own affiliates (as well as members tracked on sub-ids) underneath them.

Being the advertiser's "sole" affiliate is partially where I don't see the model you describe work. Unless your advertisers are completely unfamiliar with the digital space they are unlikely to only work with one company as their sole affiliates. Advertisers like to scale. It's why they work with networks.

What ever you decide, Post Affiliate Pro does not have a robust enough of a platform for you to launch with. Beyond that the software's ability to help detect fraud is suspect. HasOffers (know called Tune) is a way better choice. Also recommend looking at Performance Horizon Group.

Either way, highly recommend rethinking the "exclusivity" or "sole" component of your model and asking yourself why an advertiser would just go with you?

Highly suggest taking a look at HasOffers, Performance Horizon Group, or ImpactRadius. Great tracking across all mobile platforms. None of the noise or black hat issues in normal CPA networks. Happy to take a look at what you are working and jump on a call to advise.