Devante -- repeating what I said last week: "Find a shop with long experience and excellent reputation for helicoil installation in cast aluminum, then truck your motorcycle and oil change kit there."
Like Arizoni said, the outer diameter of a helicoil is a non-standard size. But I'm pretty sure your situation, while uncommon, is not unique and a "dual helicoil" solution can be fabricated. For the reasons Arizoni and others identified you should return to the original bolt sizes.
BTW it might not be a "dual helicoil" solution but rather a threaded rod with Red Loctite solution but that depends on your expert and experienced shop. I don't want to second guess them.
WRT helicoil inserts being weaker or removeable, they are neither. For instance, Edelbrock as standard practice helicoils all fastener points in their aluminum cylinder heads because the result is stronger than the surrounding cast aluminum.
WRT to using helicoil alternatives, my recommendation is DON'T. Unless your expert and experienced shop says otherwise.
WRT to prioritization of helicoil installation, my recommendation is place this before any other farkle purchase.
WRT future oil changes, your next investment after helicoils should be a 1/4" torque wrench. I use the BikeMaster digital torque wrench (
https://bikemaster.com/1-4-digital-torque-wrench.html) for all bolts. I have a 1/4"-to-3/8" adapter for the 19mm rear bolt. I only use a 1/4" torque wrench because, like Arizoni says, 4 ft-lb comes up real quick on the 8mm bolts and it has the range for the 14 ft-lb 19mm bolt. Arizoni apparently uses a "click" torque wrench which is probably just as accurate but less expensive so if he has a recommendation go with it. DON'T buy cheap because they aren't adequately accurate.
My experience with "click" wrenches is they are more accurate if you "warm them up" with a few dry runs before tightening the fasteners of interest. Do this every time you change the torque setting, especially for the low range of the wrench. And always return it to its rest position before putting it away.
PS my second favorite track is Buttonwillow. Once you get your RE sorted I suggest you first visit on a motorcycle day to understand what's happening and then another visit with an open-tracking (ie not racing) group. Its fun, addicting and it WILL improve your driving skills. Unfortunately their riding gear requirements are rigorous (ie expensive) so find some buddies your size.