Definitely go with a Milestone. If the milestone has any limits (e.g. max 5) what I would do at your place is to split the project in more phases. It’s something which will guarantee safety not only to you but to the seller as well.
I would never accept an order with delivery time 12 months, knowing that there is no guarantee that all the time spent, will be paid. I don’t think anyone would do that.
Instead I’d recommend to my client and I’d even help him split the project in different independent phases. You want the end point of a phase to be understandable by everyone in the field of the project, so if you for some reason don’t like the work or something happens with the seller, you wouldn’t have wasted time and money.
Here is a simple example
Project: Build a website from scratch for a Start Up
- Domain Research
- Design of the Website
- Choosing a Platform / SW and setting it up
- Building the website physically
- additional features, like chatbot
- Marketing Research
- Content Writing
As you can see, those are phases part of the project. On each phase, you’ll have to revise, confirm and proceed to the next phase. You can at some point interrupt or if something happens, another seller will be able to pick up from where the project has been interrupted.
Seller has the guarantee of bein paid for the part of the project you liked, you as a buyer have the safety to not waste time and money.
In your case, each phase can be a MileStone with smaller and even more specific steps.
It’s just what I would have done. 12 months is way too long to think about a single payment.
I don’t know what type of project you are talking about, but 12 months seems more like of a project requiring more individuals / team. If that’s the case, you might need to look for a Fiverr Studio gigs or open a Fiverr Business account for easier communication.
Also for such important projects keep an eye on the level of the seller, reviews, number of projects delivered, portfolio and other factors related to the wat he communicates with you.