1974 Honda 750k4 Won't Start?

I just purchased a 74 honda cb750k4 from a private seller. Rode it home and everything seemed fine. I drained and changed the oil the next morning alongside the filter. The day after that I try and start the bike but it wouldn t start. It started leaking a bit from the oil filter (I tried to tighten but it kept leaking slightly). The engine turns but the bike wouldn t start.

The gas tank seemed to be almost half full? Could it be that there isn't sufficient gas? Or is it an electrical issue?

What exactly is wrong and is it easily fixed on my Honda CBR 250R 2013?

I have a cbr250 and one day i found it laying down (possibly overnight). When i picked it up there was gas on the floor and i noticed there's a tube sticking out that looks disconnected (maybe cut clean). The bike started at first then eventually just cut out and died. Now it won't start.
What's wrong with it?
Is it an easy fix?
If it is the gas line is that easily replaceable?
Last, regardless of what you think it is, can you quote me a price of how much you think it would cost at a mechanic?

Is it ok to not start my motorcycle for 3 months?

I'll be leaving for a summer of work in Alaska. The summer months here are hot and warm - hardly any rain (Oregon). I plan to put my rain cover over my bike and keep it in the driveway while I'm gone.

Is it ok to do this? Do I need to drain the fuel before i start it back up when I come home? Any tips would be great. Thanks.

Added (1). **for more info it is a 2007 Honda Shadow Sabre 1100cc

Why are dirtbikes so expensive?

Specifically used dirtbikes. I've ridden dirtbikes plenty of times, and currently own 3 road bikes(a Honda Shadow, a Yamaha FZ1, and a Honda 300f), but have been considering buying a dirtbike recently and can't see why they're so pricey. I was wanting to just get a smaller trail bike to have some fun in the woods with, but for the prices I've seen on used dirtbikes I could easily pick up a KLR650 or similar dualsport and it'd be street legal too. Obviously I know the dual sport won't be as good on the trails, especially with it being a larger bike than I was planning to get, but if I'm gonna be spending the same amount I'd rather go for the street legal one and get the extra on-road use out of it too. Would it be that much of a negative having a larger dual sport over a smaller off road only bike?

Added (1). Ian - I'm not looking for motocross/track bikes or trying to get 20' of air, just something to zip through some trails in the woods, so softer suspension set up anyways. If that was the case then by no means would I consider the KLR. So far the biggest downside I can see is in maneuverability through the trails with a larger bike, but still can't see why I'd pay the same or more for the smaller bike just for that.

5th & 6th gear issues, motorcycle?

I have a 1984 Honda Magna 750. I noticed a month or two ago that 6th gear wasn't engaging. Then this weekend I noticed that 5th seemed to not be fully engaging. Wondering if anyone has an idea of what is wrong. Or can point me in the right direction.