There’s no need for a distinct v0.5.3 block explorer until after the fork begins, because Satoshi’s protocol recognizes all SegWit spends as valid “pay to anyone” transactions. So a Core protocol block explorer is valid for Satoshi’s protocol until when the fork-off begins.

The only thing you need to be worried about is to make sure that your BTC is stored in addresses that begin with 1. Even if you transacted through a SegWit address in the past, this would still be valid in the Satoshi chain after the fork-off, assuming that the miners don’t attempt to rollback the chain. Contrary to my misconceptualization when I was first learning about this issue, I doubt very much they would attempt to rollback the chain, because this would:

• decrease the Schelling point by penalizing some miners from joining the Satoshi chain
• decrease the valuation of the Satoshi chain by erasing some of the proof-of-work
• be more costly because the Satoshi chain would have to catch up with the accumulated proof-of-work difficulty (i.e. wouldn’t initially be the longest chain).
• penalize many of those who are trying to stay on the legacy protocol, thus reducing the Schelling point
• rolling back would break BTC’s fungibility and thus break its store-of-value valuation