I've been down this vintage audio path myself and it's quite rewarding! When it comes to brands, look for names like Marantz, Pioneer, and Technics from that era, as they were known for quality. For condition, inspect for signs of wear, especially on the turntable's needle and the receiver's capacitors.
Maintenance-wise, keep everything clean and perhaps invest in new belts and needles for turntables. Capacitor replacement in receivers is common to ensure longevity. In terms of sound, many enthusiasts, myself included, find vintage gear offers a warm, rich sound that modern systems sometimes lack. A lot of this comes down to personal taste, though.
For sourcing, eBay is great for comparing prices, but local thrift stores or specialty vintage audio shops can yield hidden gems. Always ask if you can test the gear before buying if possible.
Keep an eye on condition and trust your ears when it comes to sound preference! Would love to hear your thoughts on which models you’re leaning towards.