A couple of questions

To start, there isnt anything wrong with having 0/1 for big 3 and 4 to the amp. As long as the wire to the amp can handle the current the amp draws your in the clear. Depending on what you are looking at in the future, if the wire is not already pulled, going with 0/1 to the amp location will be better for future installs of higher power. For 100-150 on your amp, I would say there may be some good used ones out there people are willing to part with for this price, but brand new ones, this price range will only buy you disappointment from my experience. If you could give us a better idea of what kind of sound you like we may be able to give you a better idea of what to look for.

If you are limited on cash, put your money into a new set of front speakers and amp and a sub. Are you running the stock head unit?

What is the total budget you could swing right now for speakers, sub and amp(s)?

The polks are not bad speakers. I am not a big fan of MB quart ever since they were bought out by Maxsonics. Rockford is coming out with some decent stuff now but usually you have to get the upper crust, and ID has had some problems in the past few months. I dont want to come off as an audio snob, these are just my experiences. IIRC, the polk has a pretty high sensitivity and sound best with about 50watts. With that in mind you might could use one of the Alpine power packs that will give 45watts to your speakers and its small enough to tuck behind the HU. If you dont like that idea to get good SQ I would save a little more money and look at JL, Alpine PDX, Audison SR4, or ARC audio products. These are considered decently high end.

... save a little more money and look at JL, Alpine PDX, Audison SR4, or ARC audio products. These are considered decently high end.

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^^^ this is good advice.