2. Supplement the logistics of the German forces on the Eastern hook of the army with a few hundred mobilised motor vehicles.
They did this IOTL
(source), and what motorized logistics they had was critical to the initial offensive getting as far as it did. It sounds like the limiting factors were lack of an efficient system for dispatching trucks to armies on the move, mechanical breakdowns, and France's road network at the time not really being up to the task of supporting large-scale truck transport. The former two probably have opportunities for at least marginal improvement, but there's not much Germany could have done about the latter.
OTL, they did defeat the 1918 German western offensives without the American Army.
The coming of the American Army ensured that the offensive went ahead, but defeating it was done without the significant assistance of the US Army.
There's some truth behind this, but I think you're overstating the case. It's true that most of the 1918 Spring Offensives were defended almost entirely by French, British, and Commonwealth forces without significant direct American involvement, but the American Expeditionary Force did have a substantial role in turning the tide in three respects.
First, American divisions were starting to take over the defense of relatively quiet areas of the Western Front in early 1918, freeing up French and British divisions to serve as a strategic reserve. This was a relatively minor contribution at the time of Operation Michael (about 4% of the front manned by 6-8 American divisions), but had grown to 12% of the front manned by about 25 American divisions by the time of Second Marne.
Second, eight divisions of the AEF participated directly in the counterattack phase of Second Marne, where they made up most of the local Entente numerical superiority over the German forces present. And it was this counterattack that really broke the back of the German army as an offensive force: in the other battles of the Spring Offensives, the Germans had given as good as they got in terms of casualties, but the counteroffensive at Second Marne inflicted about a 2:1 casualty ratio, and more crucially, captured a significant amount of German artillery.
Finally, and overlapping with the other two, incoming American manpower replaced French and British losses and then some throughout the Spring Offensives. Even if the German army had avoided disaster at Second Marne, the roughly even trades in casualties they'd been getting in the earlier battles were a clearly losing proposition for Germany because the Entente could make good their casualties with fresh American troops, while Germany (like France and to a somewhat lesser degree Britain) was already scraping the bottom manpower barrel.