Thanks everyone for all the information, it's extremely helpful! Sorry for not responding sooner, I managed to get to my computer only now.
Would you prefer fenders to protect your clothing from splashed puddles, or not?
Yeah, I'd love to have fenders. I did ride a bike without fenders at some point in the past and I was all covered in mud as a result so I'd like to avoid that
I mean even when riding on a normal but wet road, the back wheel was taking some water up and my back was all dirty as a result.
Would you prefer drop handlebars or flat handlebars?
That I am not fully sure of. The dropped ones don't look to comfortable, I am not sure I'll be able to ride in a bent position like that but in reality I've never tried that kind of bike so I guess I'll just stop at some shop and will test drive one of such bikes.
I can't say that I am too good with mechanics. I of course can watch youtube videos and generally look at stuff and guess what it is for however I am not sure I'd risk fully assembling a bike from scratch.
At this point I think I am more inclined towards a mountain bike however I am still not fully sure. The information everyone posted here has provided a lot of food for thought and also introduced me to bikes I was not aware of (cyclocross). I guess I'll need to test-drive one of those bikes too.
Basically what kind of features I should be looking for? As far as I understand I'll need ability to attach fenders and panniers. Have the ability to switch fat/road tires. If it has suspension systems, I should look for ability to adjust it so that it performs better on the road. Is that all?
Also I forgot to mention that I am relatively tall (6'3"), which bike parameter is responsible for that and which value would fit me? Also does wheel size generally matter?
Basically I am thinking of taking the list of parameters and features I need, as well as the suggested bike models to the local shops and test driving what they have. After I get an idea of how things perform, I'll probably rethink everything again and will either buy from that shop or order a bike online. I really appreciate everyone's help and all the suggested models and I am still going through that list and analyzing the options
Btw, do the farmers and ranchers know you're planning on cutting through their pastures?
Well, those pastures do have a very worn off sign saying that it is private property however no one from the area knows what that land is and I've never really seen anyone there. I have several guesses about what that land might be but in any case I don't think that I'll inconvinience anyone by riding a bike there. If I ever meet a farmer there, I guess I'll just say sorry and will explain the situation to him. However I think that the land is either part of the tech park territory where I work or part of the half-finished (and currently abandoned) apartment complex.
My total commute to work would be approximately 4.2 miles and the muddy part is approximately 0.9 miles. However that muddy part also includes high-voltage power lines which don't look too good so I'll probably go for an alternative 1.2 mile muddy part.
Basically mud doesn't concern me that much - it's not pure dirt and most of the place is grassy so I think I should handle it without being completely covered in mud. Plus the climate here is not that rainy I hope (central NY) so I am counting on that road for at least the major part of the year. In case some big rains take place and the road gets washed out, I'll either consider using normal road or bus.
The normal road is not completely bad. I'll need to cover only 0.8 miles on it, it has plenty of space and in mornings and evenings traffic is generally slower. I do see people cycling and even jogging along that road. However I also did see accidents on that road and also there is a major university in the area so I assume many students use it. So all in all I'd rather avoid it. I know that it would be dramatically faster but it's not all about speed. The ride on the normal road will be fast and stressful while on the muddy road I'll be enjoying the ride - sun, trees, fields, birds, etc without having to think all the time whether that SUV does see me or how to avoid that car that is rushing on a huge speed, etc..
Also is it generally easy to disassemble a mountain bike to the point where greyhound/amtrak would accept it. E.g. is it enough to just put off wheels, lower down seat and put all of that in some bag?
Again, thanks everyone for all the help. I'll keep studying the links and hopefully will soon have a much more fun way to get to work