@Ron - All great questions, Ron. I'm not sure where the Ostetso HQ is but here are some general tips:
Using Upwork is an avenue you can try - I particularly don't like to lead with it because there is very little opportunity to transition to full time with those types of candidates. You see, if the person you hire ends up doing super well, you may consider bringing them in full time later - either for a sales role or a general support role. Either way, with Upwork - you won't really be able to do that so I wouldn't lead with that option unless you are 100% looking for a temp solution and are willing to invest time in someone that will ultimately leave the sales engagement with your company. Your time is valuable - so invest it now and for the future.
As far as cost - my advice is to keep it really, really simple. I recommend a monthly stipend depending on hours worked. For example, I have someone that gets $500-$600/mo plus bonuses and that person commits to 15-20hrs per week. I like keeping it simple because its scalable and predictable.
Looking at your website and what the company does, I think your baseline should be is this:
Think about how much you want to invest into this engagement over a 6 month period. Maybe it's 5K plus another 5K in bonuses.
Then think about how much delivery you want and what the metric driver is going to be. I would say in the case - 1. how much can this person spread the word about your platform and 2. how many developers would be open to tinkering with your SDK. They could be posting in Developer forums, the could be posting on LinkedIn - the could be reaching out to app dev companies. Who knows? The goal is to get as much engagement as possible. So truth is - you don't know 100% so I think you should have the person try many different things and see what works best - then tweak the compensation for what is working.
My belief is you need someone smart and creative that understands more marketing and brand awareness but has some kind of comp sci background so they have interest in the field. Of course, your expertise may say otherwise, but that is my initial thought.
Hope that answers your questions fully. If not, let me know if I can provide any more clarity.
Cheers!
Paul