Turntable advice

Topping A90 Discrete headphone amp ($599) is a best recommendation. 

My suggestion would be to look at a used VPI Classic 1 with a JMW arm, which tend to hit the market used for around $2K or less. It is truly a high-performer with a 20lb aluminum platter and very heavy plinth. The tonearm tracks very well, and the whole turntable can be upgraded - tonearms, footers, clamps, etc.

For cartridges, I would look for an Audio Technica ART9 xi. Best cartridge around $1K hands down, the only cartridges I liked after owning the ART9 cost $5K+. This though would require you to have a moving coil phono stage.

For phono and amp, if you do not look into a speaker amplifier, then look into the Pro-Ject Tube Box DS2 and Woo Audio WA7 fireflies which is an incredible tube headphone amp with a great built in DAC. 

If you play your cards right you should be able to get all this for less than $5K, but you may need to leave a little extra for quality cables as these components will absolutely require them for optimal performance. 

Technics 1200GR.  Build quality is superb, and adjustments can’t get any easier.  $1700

The Rega RP6 is a fine turntable for the money. There are lots of cartridges that will fit it without VTA problems. And in that regard, it's worth reading Roy Gandy's paper on VTA adjustment and the significance) or otherwise, thereof.

In regard to phono stages, while outside your budget at new price, a pre-owned Ear 834p is worth considering - the are extremely reliable and a great buy used at a little over a thousand dollars.

+1 Technics 1200GR!