I had an FD for 4 years and sold it to get the EK9. They have dropped in price so much recently and a really nice stock/near stock FD can be had for £4-6k.
Don't be too put off by the scare stories (except the one about fuel consumption lol), if treated well they are great cars - mine was 100% reliable as a road and track car and went over 80k miles before rebuild time.
I found the car a real pleasure to drive both on road and track, for me at least the driving position is spot on, power delivery from the twin turbos is smooth and progressive and the handling is sublime
Stuff to be aware of:
There are basically 2 things that kill a rotary engine - det and overheating. Det can be relatively easily avoided by using good fuel and having a mappable ECU like an Apexi Power FC (and good intake temps as I'll come on to), but heat is the real problem especially on track. You've got 3 things to worry about - oil temp, water temp and intake temp.
Oil temp - the stock twin turbos are oil cooled, and oil is also used to cool the inside of the rotor's combustion faces. Get a Type R model with twin oil coolers, this makes a big difference.
Water temp - the stock rad is an ok size, but especially on older cars will have lost efficiency so an upgrade to an all-alloy one is recommended, or at least a re-core. Unfortunately upgrades are not especially cheap but very worthwhile.
Intake temp - this is the key to good performance and reliability. Unfortunately the stock FD3S is quite compromised for cooling as a plain road car, let alone as a track car. The stock intercooler is tiny and doesn't get direct cold air flow, and the twin turbos chuck out a scary amount of heat into the engine bay. Luckily the stock airbox is very well designed and has quite a good cold air access. Beware induction kits that suck hot air straight out the back of the rad - not good!
Probably the most cost-effective way of improving intake temps is to use water/methanol injection (check out
Water injection systems, Methanol injection systems : Aquamist for more info) which will dramatically reduce air temps going into the inlet manifold and if you use methanol mix will also raise the effective RON rating of the fuel preventing detonation. My mate used methanol injection to great effect, he saw inlet temps of -11oC in autumn once
and got frost on the plenum!
To keep an eye on all the above definitely get an oil temp gauge as the car doesn't have one, and also get a water temp gauge as although one is fitted as standard it's crap and won't tell you it's getting hot until the damage has been done... I'd also get a boost gauge to monitor the quite complex twin turbo boost pattern and ensure you're not overboosting, which can happen with open intake and exhaust.
Edit - oh, forgot to mention to keep an eye on intake temps you can use the Power FC Commander display thingy which reads the stock Air Temp sensor.
That lot should definitely help the engine life, also use a good oil as has been mentioned - Silkolene Pro S 10W40 is great and although a synthetic has the right mix of chemicals not to damage the engine seals and o-rings (Mazda used to say only use a mineral oil but technically they are inferior to modern synthetics).
Otherwise I'd really mostly echo previous mod advice, the geometry is nicely adjustable anyway so unless you are planning on drifting or want Touring Car styles of negative camber you really just need to focus on good coilovers.
Pettit Racing in the States produced quite a useful geometry chart - I used to use the Long Track Event setup with 17"s on road and track which was a good compromise.
Finally, good trackday tyres like Toyo R888 or similar make a huge difference.
As you might appreciate, all the above plus prior recommendations will not be cheap, so your initial £4k purchase price could double or more quite easily.
Sorry for the long post - hope it helps!
Cheers,
Alex