You buy an RV-8 or any RV because they are FUN, handling is a delight, visibility is amazing, fast and do aerobatics (except RV-9, -10, -12. -15).
If you are an airplane owner you know. I don't know how much your annuals are? Are you an A&P / AI and do your own annuals?
With an experimental or E-AB (experimental amateur built), you can do your own Annual (called condition inspection) every 12 months, even if you did not build it, but bought the plane.** This can save money, but you have to put the work in, have hanger, have skills and/or willingness to learn.
** Back ground, in past you built an E-AB the plane you applied for the Repairman certificate. You were basically the A&P and AI for that aircraft you built. If you sold the plane the new owner could not do Condition inspections, they had to get an A&P to sign off. No AI is needed to sign of Condition inspections, just an A&P. Certified GA planes Part 23 need an AI to sign off the "Annual".
Now with new recent ruling you can buy an E-AB you did build, take a 2 day weekend class. After that you can apply to do condition inspection on the plane you bought (you can only work on that plane you bought). You get a Repairman certificate for just that plane.
Airframe parts are going to be cheaper, but if you need a new aileron, you might have to build it.
However it still has an Aircraft Engine, Prop. Tires.... Fixed cost Hanger, Insurance, Fuel, Oil Changes, going to be similar to any plane. RV's are efficient fast planes. In terms of MPG you can scoot along near 200 mph at 25 MPG. They are durable and well designed. Still aircraft engine care and feeding. It is a PLANE... which is expensive.
New IFR PILOT in an RV-8? I am a high time ATP retired and CFI-CFII-CFI(ME) and active teaching. I just finished teaching an Instrument student last October. He passed first time, yeah (my record still stands, all my students pass 1st time). I have flew IFR without autopilot in the 1990's all the time, including in my RV-4 (also a tandem two place tail dragger like RV-8). It had my full attention. Advanced digital autopilots were not invented for GA yet in the 90's, basic wing levelers yes. I used the IFR ability of my RV to file to depart, go through overcast or let down en-route through undercast, do approaches to high mins. I especially like to file IFR into busy airspace, e.g., Vegas or Los Angles area, in VFR condition or night. This was in the day before IFR GPS navigators and GPS RNAV approaches. I did have a portable Garmin GPS in the RV-4, but officially NAV was VOR/LOC/GS. The Dina sore days before "Children of The Magenta Line". I swear some of my customers, be they students or rated pilots for a Flight Review or IPC, have a hard time with N, E, S, W, or how to use a VOR to save their life. Instrument rated pilots are better, but most just fly magenta. I digress.
My current plane, RV-7 has dual axis autopilot, EFIS, WAAS Garmin GPS. I can hand fly my RV-7 IMC, very responsive, precise. However it has light controls and very low drag. I flew a Metro Liner 19 seat two crew no autopilot 8 hrs a day IMC back in the day. However single pilot IFR in a single engine plane is not for me anymore. Autopilot is a must single pilot, especially an RV-8, in my opinion unless it is LIGHT IFR for short periods to get to VFR. It's not a C-172. Why? For one reason we have the technology now, not available to GA planes in the 90's and even 2000's.
Second reason, an RV-8 will wind up past Vne quickly if you get into unusual attitude. My point RV's were never made to be IFR platforms as main mission, they are sport planes to have fun VFR even aerobatics, but they can serve as a good IFR platform, if you are current, competent Inst Pilot, and have an autopilot, GPS, that you know how use well not fumbling with button-knob-menu. Congrats on your IFR training. It will make you a better pilot.
As I understand it, the the 8's have a bit more shoulder room than the side by side models by the time you get two people across, but I'd encourage you to look at all the models, not just the 8. 
