We recently purchased a simple rectangular one floor home with 1340 sq ft. It was built with a solid poured concrete foundation,, vinyl siding, and lacks a brick ledge. We are a few years away from overhauling,redoing the exterior walls, and ripping out the roof, to increase the ceiling height to 9 feet and adding an addition. so was wondering if an ICF wall could sister up to the existing foundation walls? Thanks.

Sure, if the footing is wide enough to support it. If not, you may have to add to the footing width. If the ICF is just there for additional insulation plus brick support, you could go with a 4" core ICF. With 2.5" foam on either side, the overall additional ICF wall width would be 9". You can also get ICF forms with 2" thick foam for an overall wall thickness of 8".   4" ICF forms present challenges with concrete consolidation, but if the ICF wall is just backing up a structural concrete wall, then a few minor voids here and there shouldn't present any issues.

If you don't need the additional insulation that ICF provides, you could just have 6" concrete blocks or CMU layed outside the poured basement wall. This would likely cost much less than ICF. I had concrete blocks layed outside my ICF basement walls to serve as a brick ledge/support.

You can also use adhered thin brick veneer which doesn't need a brick ledge. Or bolt on a steel brick ledge. I don't see ICFs as being a cost effective for you.