Autumn planting strawberries

Not really heard of such late plants myself but so many new types are becoming available. If they're selling the plants now, then get them planted and you'll likely get a good crop by next year.
Varieties: you can stick with one, perhaps a 2nd and see which you like better tastewise and as a producer.
I space my new plants about 8" apart as they  throw off runners later and need the space. Mulch can be applied anytime to keep the roots moist and weeds under control. Just remember that the plants must be in the ground at the same level/spot they grew previously, not higher, not lower. Its a fiddle but necessary.