Owned a 180 HP S1S for 12 years and 500 hours. 160hp is ok if you are FAA std 5-10 and 170# w/ your 15# chute on.
1/2 the value is the engine/prop, the other 1/2 is the airframe.
Lyc's only go about 10 years before you have to worry about camshaft rot (sits above the crank in the air and rusts).
I suggest a 5 yr since OH and about 300 hours since overhaul- that way you know if the motor's any good and should still show no wear- PM if you want details in pain- lucky for me, other's pain- I had a great motor.
Empty weight is the next value- 800# or less is optimal, light is good.
There are 2 fuselage lengths- the S1C or basic short fuselage- limit to also Std FAA sizes.
The "long" or real S1S cockpit is longer- I am 6'1 and 230 in a chute and was ok w/ 3/4 tank of gas for acro w&b envelope.
The type of prop and battery location are the biggest impacts you can change to W&B.
Prop- fixed pitch is fine- you should get 125kt cruise at 2350 rpm w/ 76x60 prop if 180HP and a 1700' vertical line from a 180 MPH 2700 rpm 4 g pull.
Round wings and 4 ailerons- need a little push inverted vs upright, but less than anything else under $100k. You can trim it out, but most trim for nuetral pitch at 170-180 mph so you know when to pull after downlines.
Spins- inverted is safer than upright- recovers quicker- get plenty of training- you won't like it at first, but a hammerspin can kill you, as will the crossover from upright to inverted. Bill Finagin on the East Coast by Annapolis is fine, again, PM for others or get on the IAC acro news list exploder.
Roll rate- 240 deg/sec, better when snapping- you'll be the limiting factor for the first few hundred hours if you want gradeable quality.
Paint- polyurethanes are hard to repair and when they start to crack and craze there is little you can do.
The tailwheel part- well- I enjoyed the heck out of it- learned on 35' wide blacktop in an S2A, but started years back in gliders- stick, rudder, rudder, rudder.. Solo in an S1 is more fun than the S2s- they are all like trucks compared to the S1, though they may be really big 260+hp trucks. Front seat in an S2A or B is good training, but you really wear the S1s. Back seat S2 flying is not a great S1 simulator, but S2Bs and Cs do rock in their own way.
Feel free to PM.