what i've learned in 3 years with my '03 mazda6 sedan V6/5sp:
front wheel bearings were noisy when i bought it at 125k. so don't be surprised by that. before replacement it was rumbly and noisy all the time. after replacement it is vault-like in terms of interior noise. they did a nice job with NVH on these cars.
fuel pump had a weird pickup issue where it would suck air in right turns when the level was down to about 1/4 on the gauge. replacement pump assembly is about $300 from rockauto, and the whole job took about 90 minutes. remove rear seat cushion, remove access cover, disengage electrical connector, unscrew retaining ring, remove pump assembly.
timing CHAIN ftw
ignition coils (COP) start getting weak around 130k, maybe sooner. will set misfire DTCs on offending cylinder(s). i replaced mine at about 155k. upper intake has to be removed to access rear bank. not difficult or messy, as the upper intake is dry.
water pump is on transaxle end of the engine, and is driven by a short V-belt with an idler pulley ('03 - '06). when (not if) the idler pulley bearing fails, you lose water pump drive and will overheat. after '06, they eliminated the idler pulley assembly and went to a "stretch to install" belt, where you put the belt on as far as you can, then bump the starter to pull the belt the rest of the way over the pulley. i "updated" my car to the later setup rather than paying $70 for a new idler pulley assembly.
if it's had a life of quicky oil changes where they check the air filter, the intake boot between airbox and throttle body will be torn. this allows unmetered air into the engine and will cause lean fuel mixture DTCs. i wrapped mine with duct tape and drove it for another 18 months, then replaced with $20 chinese pos boot from rockauto when i did the coils.
rear caliper slides will quit sliding. it is a mazda. it is a way of life. both miatas, both probe gt's, and my 6 have all had this problem. replacement slides and boots are cheap. sometimes getting them apart is a mofo, so tackle it as soon as you see unusual wear pattern on rear rotors.
forums talk of weak clutches. at 165k i'm still on the original, so i think a lot of that is people not learning how to drive stick from someone who knows how to drive stick.
at 5 grand, i would buy that in a heartbeat if it's decently clean. in fact, if you buy it and don't like the wagon-ness of it, i will give you my '03 plus a grand and i'll deliver it to you.