Media for Speaker Placement NightMares

Speaker Placement NightMares

I am very sorry to post such a long read.

I am a beginner at home audio. I originally bought a pair of medium front speakers and a sub to match. Then I got an amp and 2 better front speakers and a center. My plan is to use the lesser front speakers as right and left surround speakers. The only thing is the Sub is that of a lesser series. The Sub has a volume control a frequency dial and a direct button. The Amp allows me to set the speakers to large or small and a crossover value. The receiver is at the back right of the room because that's where my satellite / antenna / digital projector are. I put the base in the right rear next to the receiver despite seeing most setup diagrams with it in the front of the room. My living room and dining room are one room. The dining area is to the left of the sofa. It is roughly a third of the room. There are

2 windows in the room. I will only be in this house for a year so I changing the room itself isn't an option. I just want the best sound with what I have now.

My questions are as follows:

What constitutes large and small in terms of speaker size?

How do I choose the best Crossover value for my system.

Is it okay to leave the sub in the right rear corner of the room?

There are no speakers in the dining area, should I move into that area?

Any help is much appreciated.