For Zone 5 we're pushing late, but fortunately most of MA will have a much longer fall than portions of Zone 5 I could name. :) Crabgrass dies at frost, so it's actually not terribly troublesome--it's the fact that it's probably already dropped thousands of seeds that will cause the problem next year! Getting down a good pre-emergent when the forsythia blossom and keeping up the shield through August is critical. You can either purchase a long-lasting pre-emergent like Barricade, or re-apply shorter lasting shields like Dimension to maintain the layer. Be careful and read the bag or bottle--Barricade is also available in shorter duration. I use generic prodiamine, mix it myself, and apply as a spray. For right now, you can certainly kill off the crabgrass if you want. Any over the counter crabgrass post-emergent should work fine (I have a preference for Weed B Gone with Crabgrass Control, but it's really all the same thing). If you wish to reseed, do so as soon as the crabgrass fades (this is pushing it, but you're really running out of late summer fast). Post seeding, use your irrigation system to damp the seed two to three times daily, morning and evening at minimum. A mid-afternoon cool off and dampening certainly helps a lot! Ten minutes per zone is usually good enough, but if your system is particularly high output you may not need that. If low output, you may need more. Keep that up until everything sprouts (KBG takes a full month, fescue and rye only two weeks or so). Then slowly cut back, first once per day, then every other day, making the shift around weekly. Rainfall counts, so you can skip those waterings. Next year, keep that shield up and feed the grass on schedule (May, September, October, and a winterizer if growth stops later than October 20th). Good thick grass won't allow crabgrass to grow. Pro tip: Mow your grass long to discourage growth of all weeds, including crabgrass. I keep mine at 3" and have zero weeds.

I'd wait until it hits 3" and mow it down to 2, then keep mowing regularly to encourage thickening, until the cold slows the growth. As for thin areas, you can also hand core aerate with something like a Turf Hound for small areas that need prepped. The problem with just spreading lawn soil over your turf is that you might get a layering effect which is not stable. I'd rather core thin areas--with or without topdress.

If it's Kentucky bluegrass, spotty coverage is sort of the norm. As the grass develops next year, it will fill it in. However don't expect full coverage for a good long while. If it's rye or fescue, more seed is the only way to get more coverage. The thin stalks will develop into bushier plants as tillers develop, but they don't spread. Is the soil still warm? Here in Virginia we're having cool mornings and warm afternoons and no frost forecast for the next two weeks. I'm putting a little more seed (fescue) into particular spots today and pushing it into the ground with my foot. Can you remove the straw in the areas you want to put more seed? Maybe mow it?

Where do you live? The zone isn't that helpful. SoCal is full of soil types as well as micro climates from mountains and wind patterns. What is your watering schedule? How often and for how long do you water? Why did you want clover? There is no mix of fescue and rye that will work in SoCal unless you live west of Interstate 5 on the coast. If you don't have morning fog, a 2pm sea breeze, and high temps in the 70s all summer long, then you have no business trying to grow a cool season grass. Most of SoCal should have either St Augustine or bermuda. If you are pretty successful at caring for a lawn, then you could try zoysia. Another excellent choice for the really arid areas is UC Verde buffalo grass. Any of these grasses need water only once a week in the hottest heat of summer and more like once a month the rest of the year.