Lineup

I agree with denumber50 - improving your CBs is priority #1, but unfortunately there isn't much you can do with that small a coin stack. Your best budget add could be the Champ Bailey 91 Ultimate Legend - he has 97 speed and can be had for <$20k.

Maybe the best next step after that is to focus on is getting Holt/Shazier/Tillman all up to 99 OVR. You're close with all three, but with the way your team's structured, you need those guys to all have four abilities to give you a fighting chance online. Plus, doing the solos/challenges necessary to upgrade them will add substantially to your coin stack and give you other important pieces. The Vinatieri NFL 100 challenge is a grind, but you're so close (guessing you're between 74-77) that you might as well start there and kick FGs over and over til you hit level 99. You'll get Holt up to 99, plus 5-or-so five-figure coin quicksells, more packs that will be useful for your team (either by using what you open or selling in the AH for coins) and PU passes (96, 97, 98, and 99) that would let you get, say, at least Deion (97) and Moss (99) up to 99 OVR in your lineup (Moss outright, and Deion with lockdown and physical chems).

That would then let you put abilities on RG3/Holt/Moss on offense and BDawk/Shazier/Tillman on D for now, while adding coins that you can use to gun for a CB upgrade - maybe the Jones FA master? He's pricey at ~$120k for sure, but I don't think you can get a significant enough upgrade by spending less - you'll have the same problems with speed if you, say, tried powering Asomugha up with his 94 Theme Diamond.

18K is not a lot of coins - but my first suggestion would be upgrading those corners, by this time in the game there are 99 speed receivers on each game and if they don't match that speed it'll be hard to not get burned overtop