Long time lurker, first time poster.
@Mischief,
Dirigible is pretty much on target with his response. I’ll expand upon his post a bit further with my own personal experiences, as I do not own any meaningful quantities of any 3* covers as yet (I have enough to get myself into trouble, but not be dangerous in significant manner).
First and foremost, unless you plan on pouring cash into the game, silver (standard) tokens are your absolute best friends in this game. At first, they will be your primary source of progression in the game and then later become a complement to tournament 2* cover prizes.
As you mentioned, you will hit a wall fairly quickly in progression on the Prologue. When that happens, work the SHIELD training for basic 1* covers and grab the low hanging fruit from tourneys. Work the Lightning Rounds (every 2h Tuesdays and Wednesdays) for the 25 point ISO and 50 point silver token prizes. Bow out as soon as you hit 50 points.
Eventually, you will gain enough 1* covers from silver pulls and ISO from easy sources to push farther on the Prologue. You should be able push all the way to the last chapter of the Prologue with a 50 IM35 + 50 MStorm + 40 MWidow (with maybe the only exception of the Symbiote Showdown fight at the end of Oscorp to open the final Dark Avengers chapter).
Next, look to the major tournaments. As Dirigible noted, the goal here is not to attempt to win, but to score well enough to win 2* covers. With a maxed set of 1* covers, 200th place for the 2* cover of the week should be easy to obtain. The real goal here is to land in the 46th - 75th prize bracket to win 1 of each color of the 2* cover of the week. As each major tourney is played twice consecutively, you can easily win up to 6 of the same character’s covers each week. Consistently placing in this bracket is necessary to build up your 2* arsenal. This prize bracket can usually be reached at about 300-350 points. A couple of notes on staying under the radar… fight a few times early to place on a leaderboard and then wait until the last hour of the tournament. You will get beat up a lot, and this is fine. By pushing in the last hour, everyone who is fighting for the coveted 3* covers will have long passed you by (even the late entrants) and you will be too meaningless to pick on. Next, watch your ranking as you climb up. Do NOT fight any more than you absolutely must to reach the 46 - 75 bracket. Ignore progression prizes, and avoid the lure of the 50 HP prize. The three 2* covers are more important than the hero points. Once you reach about a placing in the 50s, STOP. Do not get greedy and risk the wrath of the people fighting over the 3* covers because you racked up too many tournament points and now look like an easy source of points to them. Again, DO NOT fight ANYONE at this point. SKIP all retaliations opportunities. Do not get into a back-and-forth retaliation war with anyone as you will almost always lose, in both time and points needed for placement. ONLY fight if you fall out of the 46 - 75 bracket, to get back inside of it. If you stay under the radar, most opponents outside of the ones using this same strategy, will leave you alone in the last 30 minutes of the tournament and allow you to walk away with the 2* covers. (Also note that ranking 150th or better in your bracket will also award 50 HP as well, allowing you to eventually by roster slots for all of the 2* covers)
Using this strategy from when I started this game, I have obtained almost a complete set of 2* covers, using only 2* teams. Two weeks ago, I finished off my collection of Original Widow covers, last week, Moonstone, and tomorrow I will collect my last CStorm covers.
I hope this information helps you break out of the 1* stage, as the game is much more interesting at the 2* and beyond levels.