yeah dammit!! 3.45 all the way baby!!!! (owner of a EB XR6...)
2, 3 & 4 - Do you know when it had a tune last? If you don't know, I'd personally change the lot - plugs, leads, distributor cap and rotor and don't forget the fuel filter too.
yes, new plugs, leads, dizzy cap and rotor are all the first things to give trouble, also replace fuel filter (make sure you put it in the right way!!)
a 2" exhaust is smaller than stock!!! get a 2.5" mandrel bent one, get the shop to check the cat out, they have a habit of melting inside which reduces power. get a new cat (normal one, hi-flow dont do much IMHO) and extractors as well if you have the money.
change oil and filter, and also auto oil and filter, you might as well it probably needs it anyway.
after all this take the +ve terminal off the battery (leaving the ignition on) and leave it off for about 10-15 mins, then turn the ignition off and refit the terminal.
start it up and take it for a strap!!!
i have a manual EB XR6, has 135,000k on it, has Mock extractors+2.5" exhaust, 16degrees base timing, pod filter and running on BP ultimate (not forgetting a stereo that weighs at least 50kg)
i did a firstname.lastname@example.orgMPH (wheels say stockers do a 15.7) at willowbank (a slightly uphill track) so yours should go well when you get a decent exhaust and new service items on it!!!
LOVE THE XR!!!!