In my question, a space fabric "plane" consists of many "islands" strewn about, and any point of the plane which isn't part of an island is "bottomless". The "gravity" at a point is affected by the curvature of the fabric at the point, in addition to mass.
Each island is "circular" or, to those inside, spherical with interior diameter 50 ly. The islands end asymptotically (the closer to the edge, the stronger the pull towards the edge and the faster the pull increases). Before the edge (i.e. slightly more inside) of the island, there is a border of "heightened" fabric (approaching the border, a ship would need to counter gravity). An island's interior is relatively flat (although there are some areas of slightly heightened or lowered fabric.
Travel inside an island is with FTL; it takes about 3 days to traverse an island (i.e. go from an edge border point to the opposite). To travel between islands, the inhabitants of Islandia use fabric-casting devices mounted on large ships (abount 1.5 km long at minimum), called fabric-caster ships (FC ships). When "on" an island, it lies on the island, but if it goes over the edge border of an island, it "takes off" with cast fabric (the cast fabric functions like a platform over the bottomless pit).
After that, they can't see outside their fabric "normally", but a FC ship is typically equipped with a navigation device to "see" islands (but not other FC ships; their fabric is too small to detect). They also can't communicate with an island until they "land" on it. If an FC ship's fabric-casting device fails while the ship is not on an island, the fabric is destroyed.
The islands are about 3 to 4 months apart.
A FC ship casts a fabric, spherical to those inside, about 50 km in diameter. Unlike island fabric, however, those fabrics end abruptly. Ships which travel with an FC ship travel close to it, to avoid falling off. Ship-cast fabrics rarely collide, because their heights usually differ. When they do collide, they destroy each other along with the ships on them. For this reason, FC ships adjust their heights so they're not the same as each other.
In the plane, there are two warring states (political entities). The territory of each is constituted of many islands, about 100 in number. There are 15 front islands on each side. Each side has about 1,000,000 military crafts (including support crafts, but not including fighters). The ships fight slower than light but can jump into FTL with recharge time 60 minutes. The weapons are mostly projectile weapons. Projectiles travel far below lightspeed (about 150 km/s on average).
I think the major problem which puts an attacking fleet at a disadvantage is that attacks are far-flung expeditions; maintaining a supply line that long is very expensive. The defenders have clear advantage. Another thing I thought about is if a side would attack the capital right away (fleets are hard to stop when travelling on cast fabric) or island-hop little by little starting with front islands.
In short, my question is
How would warfare be conducted in such a setup?