so cloud base must be at least 1000ft
you can not fly higher than 500 ft ...but none of the above applies if you stay below 250 ft...
You're mixing rules from Part 101 and 91. (You're also forgiven, since you live outside the FAA's jurisdiction.
) There is no minimum altitude to maintain under part 101, only a maximum. If you have a cloud base at 510 feet, you can "fly" at 10' AGL all day long. I'm not aware of anyone who flies a gyroglider at 500' AGL or higher. You'd be somewhat limited by the required length of its cable (over 700' at a 45-degree angle), the resulting weight of the cable, and the ability of the glider to lift that weight.
If you stay below the top of any structure within 250 feet horizontally, you're fine, provided you don't obscure
that structure's obstruction lighting.
You can also fly legally at an airport with a waiver, but that requires advance notice to the FAA of date and time, and a NOTAM will be issued.
Part 101 is an odd set of rules to apply to a gyroglider, but the FAA had no other place to dump us. A boom trainer that never gets more than 4' AGL doesn't represent the same hazard to aviation as a business that tows tourists on kites behind speedboats, but the same rules are applied.
I see a couple ways around this. A gyroglider is only covered by Part 101 if it is tethered throughout its flight. If the glider was configured to be safely released, it could be released for landing, and could then fall under
Part 103 (if under 155 pounds) or
Part 91 (requiring a glider certification).