So, you are trying to recreate what major performers do on a million dollar budget with a $8,000 budget? Major artists use LED video walls and rarely projectors, but when they do it is $100,000 models. This isn't a knock, but a reality consideration.
The problem being what you already mentioned - light output.
In a completely dark theater, you need 18 lumens per square foot of screen space. In a normally lit boardroom, you need no less than 80 advertised lumens per square foot.
You don't go with 8 foot wide, by 10' tall screens unless you are running everything in portrait mode, which I suppose is a possible way to do things. In fact, it may be the only way to do things if you want to go that tall, and keep things narrow, and maximize performance.
So, let's say 7.5' x 10'. Which is a 3:4 setup. Using a 4:3 projector on it's side is the only good way to do this.
That's 75 square feet per screen. Using 80 lumens as a minimum target, that's a 6,000 lumen projector. Not any are out there which can meet your budget, but there are some that come close. As well, you may want a lot more light output than these offer, but this is what the budget delivers. Be aware that if there are DLP models which claim greater brightness, they can't do so with accurate colors. So, stick with LCD.
This is the list I would pull from...https://www.projectorcentral.com/projectors.cfm?g=1&hide=0&st=1&exp1=1&r=&br=5000&br=10000&c=&w=&db=&ar=4%3A3&zr=&wt=<g=&ll=&wr=&dt=1.0
It's worth noting that I pushed this list up to $2,500, and I think the laser model from Epson is a nice option..https://www.projectorcentral.com/Epson-PowerLite_L610.htm
This model will remove the need for replacement lamps (at $250 or so each) and gives about a 10% performance jump. So, long term, it ends up being less money, brighter, and more reliable.
- Theater, whole house audio, and technology consultation during the build and installation process in the Washington, DC metropolitan area.