Should I isolate the ground and neutral in the 30A safety switch box or keep them bonded until the sub panel it is feeding (as service disconnect)?
Ground and neutral only meet at one place, and that place is the main panel

You must keep ground and neutral separate everywhere but the main panel -- this is the cardinal rule of how grounding works.  As a result:


Land the feeder grounds on the terminal block/bar in the safety switch, bonding it to the case with the green screw
And wirenut the neutrals to each other, but do not connect them to anything else in the switch


That way, the safety switch case is grounded, and the grounds and neutrals run through to the subpanel, but ground and neutral do not meet here.

You don't really need the safety switch -- there are cheaper ways to make this as safe as you desire

While the safety switch does provide a disconnecting means for the structure, it may be less costly to put a QOM2100 in the subpanel (all but the smallest QOs are convertible from main lugs to main breaker or vice versa) and use that as a disconnect instead.

In order to keep some dunderhead from turning the subpanel back on while you're working on it, what you can do is get a lockout device for your main panel and then use a thin-shackled padlock to lock out the breaker for the subpanel while you're working on it, keeping the key in your pocket while the work is taking place.  That way, any miscreant who wants to zap you will have to bust the lock first, which should be enough of a clue to someone who's not truly malign in intent that they shouldn't be doing that!