How many cc engine do I need?

I'm new to motorcycles. I'm 6'4 and weigh 350 pounds. My Girlfriend weighs around 150. We will normally be riding it together so I need a motorcycle that can easily handle 500 pounds on it at highway speeds. I'm interested in the Honda VTX 1300. Would that be enough? Could I go with a lower cc engine and still handle 70 mph easily enough with 500 pounds?

Added (1). Would a 750 cc engine be enough? Also considering a shadow aero that I'm looking at. I like the Honda's and I hear they are reliable.

Added (2). I'm looking to spend as little as possible because I do not have much money to spend right now, but other good motorcycle recommendations are welcome.

Weird motorcycle voltages

So I own a 97 Honda Shadow 600 vlx, 11,000 miles it's got some werid problems. So it's been misfiring when underlow rpm usually when going up a steep hill in to high of a gear or sometimes coming from a stop. Also one morning the headlights started to get really dim like it wasn't charging. My voltages are really werid too. At low idle the voltage reads 12.8v. At high idle with choke on the voltage reads 14.4v. If I rev it higher the voltage drops to 13.5v. Battery voltage reads 12.5v and battery voltage with key on reads 12.1v

Loss of power in Low RPM?

I ride a 2011 CBR 250R，Recently I have been having a problem with losing power during first and second gears around the low-mid RPM's. It happens when I accelerate at a quicker speed it feels like the power cuts (which engine braking occurs) and then it accelerates again after 1 or 2 seconds.

It usually occurs when I have 1 or 2 bars of fuel left so i believe it might be a problem with the fuel or petrol. I have been filling my tank with the normal petrol required at well known gas stations in my area.

I have recently had this problem but after servicing the motorcycle (a few weeks ago), it was a problem with the air filter being very clogged and dirty, after servicing it was fine, and then this started happening recently.

anyone have any idea what the problem is? I did email honda and they said my chains and sprockets may be the cause to it and they need to be replaced, I'm looking to replace them but I'm afraid if after replacing them, the same problem will still occur.

New to riding, 2015 Honda cbr650f?

So I just got my first bike the other day from a dealership. They have done maintainence on it so I don't think it's anything mechanical with my bike. But I've noticed when I come to a complete stop in 1st gear the bike just shuts off on its own. I've stalled it while shifting into 2nd and third a few times and it doesn't feel like its stalling when this happens, the bike doesn't lurch forward or anything, it simply just shuts off. Any ideas what I could be doing wrong? Or any tips on how to come to a complete stop without this happening? New to riding, 2015 Honda cbr650f

Honda cbr125 bad vibration?

I have a Honda CBR125r 2006 . The bike seems to run fine and pulls really well for a 125 however if my RPM's go over 6-7 k it vibrates like made, seems to be engine, but not sure. Any ideas?

Motorcycle speedometer cut off suddenly?

So whilst riding on the road I glanced down and found my speedometer was completely off, The Bike was still running fine, I could shift gears, accelerate, brake just fine, just the speedometer looked as if the bike was off. I stopped on the side and turned the bike off and back on but it was still completely lifeless.

The turn signals weren't working, The hooter wasn't working and I believe the brake lights weren't working either. The low beam and high beam lights were fine though. I'm planning to get it seen in the next few days but just wanted to see if anyone might know the fix to it if it could possibly be just a small issue or something might just be unplugged or something.

The bike is a 2011 cbr 250R and it was recently serviced only last week at Honda.