I think Resilient (DEX) at 5th is reasonable, since it boosts your DEX while giving you something else too, though I might rather have the Halfling feat Second Chance for that --- would give you a way to cancel crits, which AC can't do. On the other hand you will eventually have a lot of things competing for your reaction.
Something to think about: When you are Fighter 5 / Rogue 1 and leveling up to 7th, is there a feat that's worth more to you than cunning action? If not, just take Rogue 2 instead. And then, if you're Fighter 5 / Rogue 2, is there a feat worth more to you than three cantrips and three spells known? If not, just take Rogue 3.
If your really focused on being hard to kill, you might even want to consider going to Fighter 1 / Rogue 8, for all of the great defensive benefits arcane tricksters get at those levels: Shield at Rogue 3, Uncanny Dodge at 5, Evasion and Mirror Image at 7.
Note that magic initiate warlock will only allow you to cast your spell once a day, even if you later gain spell slots from arcane trickster, since you won't be a warlock. So you can potentially get 3d6 damage for a few rounds (if you get a reaction attack every round). It may be worth it; cantrips are nice to have, and it would give you a little bit of "burstiness" for the big fight of the day, as opposed to slightly higher damage all the time, as from maxing DEX.
You could consider Magic Initiate (Wizard), which would give the cantrips plus a spell that, once you get to Rogue 3 you can cast with your regular spell slots. You could take Find Familiar, which you would rarely need to cast more than once a day anyway, or take Shield, which frees up your "any school" pick at Rogue 3 (although RAW you can't cast it with your hands full without war caster). No point in taking Mage Armor before your DEX is maxed, but you could take that with an AT pick later if you wanted.
I'm not sure I'd take either of those at 7th over just the +2 DEX, though.
If you are playing the tank and staying next to enemies on purpose (as opposed to using cunning action disengage), then you should probably take Sentinel at some point. It complements riposte, since you use it when they attack somebody else, and gives you another way to get an off-turn sneak attack.
Lucky is always good, and fits well with a Halfling.
I think what I'd probably do if going to Fighter 5 first is take Second Chance at 5th, then go Fighter 5 / Rogue 3 (take Shield), then grab +2 DEX at 9th and your favorite feat at 10th: maybe Magic Initiate (Wizard) for Find Familiar or Mage Armor, maybe Medium Armor Master, maybe Lucky.
Then I'd be Fighter 6 / Rogue 4. If I'm leaning hard into tanking, I'd probably go Rogue 5-7 next for Uncanny Dodge and Evasion, as well as Mirror Image (and trade up a spell for Shadow Blade too; it's just too good not to grab, especially since you have two attacks). Then get to Fighter 8 / Rogue 8 for two more feats.
