My immediate thought is that the challenge you've taken on is immense, and you're going to need in house support for the non-technical stuff as much or more so than the technical part. Getting the right people engaged and on board will prevent this challenge from going from tough to impossible.
The people part: based on what you've shared, the areas you're going to need support and help in are:

• Sponsor from someone in leadership. Everyone wants a shiny dashboard, no one wants to pay or wait for it. You *need* someone who calls the shots to champion this project, both to get key decisions made that have to come from the top AND to go to bat for you when people realize that a BI platform doesn't materialize from thin air.

• Contracts and/or Budgeting specialist to take on the budgeting of licenses and keep track of Microsoft's ever-changing cost approach. This should help to inform decisions like whether to use AWS or Azure. From a purely technical perspective, I prefer the latter--I simply find it easier to maintain everything on the same Microsoft stack since the tools overlap so well.

  • This isn't a one-and-done kind of thing--Microsoft seems to change its mind constantly on how they want to package and charge things. Don't try to do this by yourself on top of working through all the technical stuff or your brain will explode.

• Coordinator -- you're new to this company, which puts you at a disadvantage because so much of figuring out what a BI platform should have is actually about figuring out who the key players are and getting them to explain what the business needs are so you can help to solve them (when you can.) It's lots and lots of meetings and listening and making many notes on sometimes conflicting information--you're going to need some kind of very organized and connected person to help you coordinate and get in front of the right people.

• Security-- depending on how complex and layered the access rights are, you're going to need help with figuring out the security logic. Is there someone in your IT team who does security and maintains things like azure active directory? Could they be commandeered to help with analyzing or at least providing feedback on how you're tackling security?

These don't all have to be full-time roles by any means, but they would fill in the gaps in your knowledge set and free you to work on the technical part, which is going to be a substantial amount of work all on it's own. You probably want to hire at least one more person with strong Power BI skills to work underneath you.

Once you've compiled your BI strike team, lock yourselves in a room for a couple days and map out who the key players are, how much it will cost, how long it will take, what the key times are that your development time frame should take into account, and who needs to sign off on whatever plan you guys came up with. There are too many intersections between people, money and tech here for you to figure this out on your own.

Hire consultants? We did--it was awful, and I encourage everyone to avoid it if you possibly can. If you do go this route, collaborate as much as you can on the technical build and make sure you have specific expectations in your contract about documentation, both for your desk manual and within any SQL views or data model details/naming conventions.
I'm making an assumption that your company does want to ultimately manage the BI stack independently, and as long as that is the case you really want to do as much as possible in house, especially if you're not running in tight deadlines. This is a perfect learn-by-doing opportunity. If there are other staff that also know Power BI & SQL, they've already got the core skill-set. Azure tabular data models are mostly just bigger Power BI data models with better toys.

There's always this assumption that consultants will provide a superior product--in my experience the opposite tends to be the case. You get a better result if whoever is working on it has a vested interest in the quality of what you're putting together. Obviously technical skills matter, but those can be developed (and it's cheaper to develop them if you have the motivated employees than to pay an external team to miss the mark.)

I'm going to stop now since I've already written a novel--but if you have other/more specific questions, I'm happy to field them.

I would set up a snowflake instance. You can have a separate database for reach client. Then put looker on top of that. Looker has more scale ability than tableau with less overhead. Snowflake will allow you to cram as much data as you want into it and be able to pay only for that, scales perfectly with multiple clients and different needs. These tools are super simple to set up and maintain. They are also designed to meet the requirements you are setting out. Should you have any interest in it, I would be glad to go into more detail.