Assuming that's a mel culture. If you follow proper mite control procedures (predust FFs with Calcium Plus, use mite paper or DE moat between cxs, disinfect cups etc between uses, store media in the fridge, don't seed from any cx more than one month old), any mite issues will be controlled and there is no reason to stress about them.
If you don't follow mite control procedures, FF production may gradually dwindle in successive cxs until you'll have to get a new starter cx. Not a big deal, but since getting clean usable cxs is something of a challenge (and expensive) it is worth controlling mites.
That's a lot of larvae for day 28, at least compared to mine which are pretty burned out by that point. Describing your cx procedures in detail might be useful if only to get some input into possible issues that are not causing problems right now.