In my experience the bottom three tasks do not change without completing them. I thought they changed at weekly reset, but I think that just coincided with a patch that might have changed them. Through the most recent reset my bottom three tasks remained the same. The top task however rotates each day.
For your specific tasks
Win 10 invades. Don’t be afraid to use your find another to make sure the person is roughly your level. That is not a guarantee of anything, but it certainly makes it more likely you will fight someone with similar team levels. Try to just do a couple a day, they don’t have to be in a row, so you should stack up 10 wins eventually. However that one is fairly common for that slot in my experience, so you might end up with it again shortly. The other advice on improving your team given here is all good.
Contribute 5000 to a guild. You mention you are not in a guild, I would certainly recommend you give that a try. Guilds boost your gold income from your daily login, boost your masteries, and provide easier access to keys / gems / maps. I am not sure if the 5000 has to be contributed all at once or over time. If it is over time, maybe just 1k a day for 5 days (or 500 a day for 10 days) to knock out the task. I have not seen this one repeat, so once you are past it, hopefully it stays away for a while. As to gold farming, the Arena really isn’t a good place to do that. You pay 1k for a maximum of 1.5k payout (barring gold gained from battles which is relatively small). Invades make a lot more money. Also, level your kingdoms by doing the quests within them. Challenges too if you can pound through those. The more kingdoms you have leveled the greater your chance for multiple tributes which will get you gold, keys, and gems. Finally, watch for the task that says to open a kingdom (it shows up in the top slot). That gives you 2500 for opening the requested kingdom which early on will actually make you gold, and later on will greatly defray the cost.
Broaden your mastery levels. The mastery level ones seem bugged. I have one that says I need lvl 10 in any mastery which I have (and received after receiving the task), but it refuses to complete. Most likely another batch of task corrections will be in the next console patch. You probably don’t have much choice but to ignore this one for now unfortunately. About the only thing you can try is spreading your points around as you level, it might very well want you to gain a point in every mastery over what you had prior to receiving the task. Or maybe in a few or something. Try spreading those points around to see if you can make it go away.