Hello! First post after browsing a ton of threads on here and finally deciding I should just join the discussion

(I think this is where to post but if not I can post elsewhere with your guidance)

I am buying a bike that I will use primarily for exercise and riding around town. I hope to put a bunch of miles on it in like 5-15 mile rides. I live on Whidbey Island, WA currently and the terrain here is rather hilly with long gradual hills rather than short and intense ones. Soon, I hope to be moving to Seattle where you experience more intense hills and such and the bike I buy I'm hoping will work well in both environments. I'm really thinking I'd like an IGH on more of a hybrid frame; the Spot Ajax, Van Dessel WTF or Scott Sub 10 are bikes I'm extremely interested in, though out of my budget. Ideally, I'd like to spend around $600-750 on the bike but make sure I'm not painting myself into a corner and have nice options to upgrade down the line; it's a bike I plan on keeping for a long, long time and I don't envision myself buying a dozen bikes over the next 5 years but I guess everyone says that, right? Here's what I'm thinking of doing and would love your feedback on.

I am in love with the Stop Cycles Proletariat frame. Read good things about the frame, love the looks and they are good guys who have been really helpful and accommodating whenever I've spoken with them. As they no longer make the bike and shops do not have any completes, I'm sort of SOL. However, what I am considering doing is buying a 2011 Novara Big Buzz (18-speed SRAM, disc brakes) I found on Craigslist for around $450-500 with fenders and a rear rack, but also buy the Proletariat frame. I would then take all the components off the Big Buzz and transfer them to the Proletariat, leaving me with a Novara frame and a ready to rock Proletariat. The Proletariat has horizontal dropouts, but my plan is to buy a dropout adapter to mount the rear derailleur to and then down the line buy the IGH and be done with it: I got my complete Proletariat, I just did it in the most unconventional of ways. The Proletariat frame/fork is currently $299, combine that with the Big Buzz for $450 and I'm in for $750...which is right in line with my budget. I may even discover that I really like the derailleur setup and pass on the IGH but at least with this frame I have the option of upgrading, whereas if I got a frame like that Big Buzz with vertical dropouts I have no option to switch to IGH.

Anyone done something similar where you've ridden derailleurs on a horizontal dropout bike? Converted to IGH down the line? Do you think this solution can work...or, would you just avoid it like the plague. If I could build the bike from parts rather than pillaging the Big Buzz I would but I'm just not seeing a way to do that if I can get it all from that bike on Craigslist for that low price.

Thanks and I appreciate any/all feedback you have!