I hate to say it, but to cut to the chase I think you need to put up with your stereo for a while.
If you had the bose, I would say unplug it from the sub, because the bose amp (IIRC) is wired into the other speakers too. I think you will be fine to get rid of the sub, you can unplug it at the sub or easier at the amp. If you're subwoofer is bad, you can read up here and see if you would like to find a replacement aftermarket subwoofer, maybe that's something down the road.
https://www.tahoeyukonforum.com/thr...woofer-drivers-to-fit-in-01-02-oem-box.74175/
I think your friend is close, but completely backwards. I thought that bypass harness was so you can use your factory bose amp with an aftermarket head unit, neither of which you have. Someone else will have to verify.
Those speakers are listed as 300w max and 40w nominal. Your factory head unit does not have enough power for those speakers. You will be able to listen at low volume, but if you try to turn it up at all, you might damage your new speakers. Its easier to blow speakers with too little power than too much.
SECOND PART: just unplug the tweeters. Your 2 way speakers are already covering those frequencies.
MY SUGGESTION: It sounds like you are on a REAL tight budget here. Your stereo will sound better once you get an aftermarket head unit, even if it was with just your one pair of speakers (which you could put in the front for the time being). I would start with a head unit (probably used if budget is that tight, ebay, craigslist, or forums). You should be able to find a decent used one for under $40, and a little less than $100 for a new one. There are head units that will push 50w, but those are almost all max wattage, and will still underpower your speakers.
Figure out how far you want to go with your entire system. I would suggest finding another set of speakers. Components (different speaker for lows, mids, and tweeters for highs) will sound better than coaxials (the 2 ways you picked up) if your budget allows it. The components/better speakers would then go up front. If not a better pair, then what would be best is to try to pick up another set of the pioneers you have, or something similar in power range. Those are 40w nominal 300w max. I would look for a small amp for two pairs of speakers a 4 channel amp with low wattage, something like a 4 x 40w RMS up to a 4ch x 75W RMS, (even new you can find one for less than $100, and as low as $50). It would be powerful enough for your system, but still small enough it wouldn't be a big drain on your electrical system, (which means upgrading other things like alternator, speaker wiring, battery..).
Having said all that; since it sounds like it is going to take a little bit for you to save up any ways, I would REALLY SUGGEST that you figure out what you want to do with your stereo. What your end all goals are and what options you want with your stereo. Start looking around your local Craigslist, ebay, here, and crutchfield. Crutchfield will give you more options than anywhere, they will give you install support if you need it, they will include the little pieces you need to install, and I'm pretty sure they price match. See what is out there, your options are, what prices are going for, BUT DON'T BUY ANYTHING ELSE.... Black Friday and Cyber Monday are a month and a half away. You will find some of the best deals all year long, and will get new equipment for the price of used. Its not difficult at all if you do it yourself, but you should be able to find a place locally that will install for cheap enough. I would think what you should really be looking for is a package deal on craigslist; head unit, amp, speakers, wiring, (that you know works before you buy it, for roughly $100) and they might even help to install to get a sale . Unless you can find something like that, I would wait it out a month and a half.
