What's the source for amailut (trying hard/ toiling) to learn Torah? Is there any benefit to try learning Torah on your own without help, when you can learn Torah through asking others and looking things up (which is a much faster route)?
You can work hard and ask others for help.
Once the Alter Rebbe called the Tzemach Tzedek and offered to grant him a gift – a blessing for an understanding of Torah. The Tzemach Tzedek declined the offer, saying that he wanted to acquire Torah through toil. He later regretted this, for whatever levels of Torah he could have received as a gift from the Alter Rebbe, there would always be additional levels to toil for.
For more information about toiling while learning Torah, see http://www.lmaanyishmeu.com/pdf/195%20-%20Toiling%20in%20Torah%20-2.pdf
The Gemara in Brachos 6b says "Agra Dishmita Svara"- The reward for learning is in "svara"=reasoning meaning the greatest type of limud hatorah in schar wise in merit in learning something that is more intellectually challenging.
as for the second half of the question, generally you will get better understanding when learning with a group than by yourself. this is true for most disciplines, secular or religious.
Pirkei avos 5:25,26
Ben Bag Bag says: "turn in it, turn in it for everything is in it. Reflect in it, grow old in it, don't turn from it for there is no greater measure than it".
Ben Hai Hai says: "according to the toil is the reward".
You can never learn enough. And the more energy you put in to understanding and exploring torah, the more rewarding the experience will be.
I doubt that these Rabbis encouraged learning only on one's own. That contradicts a main theme of the mesorah, outlined throughout Pirkei Avos. Learn from others when you can ("Make for yourself a rav", ibid 1:6, "Who is wise, one who learns from every man" 4:1, "have your house be a place for sages, sit in the dust of their feet drink their words with thirst" 1:4). Think over what they say, toil in it. When you cant learn from others, learn still and work to understand torah.
Learn however you can, as much as you can is the message, I think.