Very valid points on Engine techs and ramming, but the solution sounds very much like your own fleet of highly maneuverable MC30s. Yes, the Rieekan player will have an enormously difficult time ramming them. MC30s are a fairly hard counter to the smaller ships, so that's not surprising. They can be outfitted to kill them in one shot and have the speed and maneuverability to avoid them. An ISD, even at speed 3, is going to have a very hard time avoiding that CR90.
Another option is to bring high-hull fleet and just take it. As long as these corvettes are out, the exchange benefits ISD player (as it also removes activations from Rieekan and makes it easier to target already activated ships). As a matter of fact my regional list originally was created as a direct counter to Rieekan.
Hmm... Depends very much on the upgrades. In a strictly-ramming scenario, a naked CR90B vs naked ISD-1 actually has a (very slight) advantage in that trade: 39pts/4hull < 110pts/11hull. That said, Motti on the ISD swings it back heavily in the ISD's favor. In practice, the value of the trade will actually come down to relative upgrade cost: whichever ship has the greater percent of its cost derived from upgrades is the loser.
That's why I don't do the ET cheese when I run Rieekan's corvettes: it kills your return on investment points-wise while simultaneously committing you to the outright trading strategy. SW-7, by contrast, not only improves your trade-up value significantly against the bigger, more hull-efficient ships, but is much easier and more reliable to use, and you retain the ramming option if the situation warrants it.