What you have drawn is totally doable but probably more complicated than necessary. Orientation of the job makes no difference to the infusion part - but overhead is always a pain. It looks like a solid single skin laminate without core. What is the material the boat is built from? E-glass/polyester, e-glass/epoxy, carbon/epoxy?
If this job came my way I'd go first to vacuum bagged wet-layup with epoxy - or open molded vinylester - but probably epoxy unless a gelcoat repair too. Its less demanding of perfect vacuum and easier to use - and you could do multiple holes with one resin mix and wet-out. Structurally, bagged wet layup is very similar to infusion and its easier to control. If there is no core, you could (in theory) do the whole thing from one side. A piece of hard-ish (depending on curvature) plastic stuck over the back (inside usually - because access is harder) and secured with tape and covered with a vacuum bag stuck to the hull can be a good former. Then you can do the whole thing from the outside (drill a few tiny holes near the edge of the repair through the hull to tie the bags together or connect the bag to the pump inside and outside) - then cure and fair. You can wet out a big sheet of material between plastic sheet and cut staggered stacks to your pattern. A 15:1-30:1 scarf is common - or whatever your engineer says - for smaller holes, the scarf slope can be less especially if its in a low-load area.
Doing it from both sides is better - but not by a ton if there is no core - it just feels neater mostly! Sometimes avoiding inside grinding is a big deal. Your only real reason to consider infusion is that doing a bagged wet layup of 12mm of material is not ideal - its hard to get air out and lots of layers! You can of course break it up into two cure cycles and do 6mm at a time. If it were a much larger repair and the boat was built using infusion - then an infused repair with matching materials would be a much more attractive idea. So I guess it totally depends on the boat, the location on the hull, access, engineering, materials, etc...
If you have never done infusion before, you will be more likely to get a good result with bagged wet-layup - its just easier to get right.
Do you have any pictures of the holes?