I'm a little way behind you. I see Kenny completed the missions. I'm on about 58/70, or something like that.
You can replay any mission at any time via the pause menu, but I'm not sure if you can replay the big heists - the ones where you're effectively doing 3 or 4 missions. If you want to go in using sleeping gas but went in guns blazing first time then presumably there isn't a "get the sleeping gas" mission for you to replay. Might have to start the game anew?
I'd be up for replaying the whole game, tbh. There's a few things I'd do differently.
I did the Lester missions too early, in retrospect. If they generally give you a 50% boost to your savings then it's probably best to leave it until you have a lot of savings - so don't buy properties early, don't spend much on clothes/cars, and leave the Lester assassinations until late in the game.
I currently have one (or maybe more?) Lester mission remaining. I actually did it (climb up a massive crane in a construction site, then shoot down a helicopter), but my characters only had about a mil savings between them. The very next mission I did was a bank job that gave each of my characters about half a mil each, and I realised I'd have been much better off doing those missions the other way round. So I reloaded a save from an hour or so earlier and re-did the bank job, but haven't done the assassination job yet. I could earn decent money doing it now, but I imagine I'll earn a lot more if I leave it a few more days, and do it at the end of the story.
I'm crap on the collectibles stuff. I found one mystery letter thing at the top of the cable car ride on my first day playing, but I'm not sure what that's for and it's the only one I found. I think it was 1 of 50. I've not found a single UFO piece. Again I think there's 50.
I've only flown under about five bridges. I could happily spend a few hours flying around going under bridges, but I know I'd end up frustrated when there's 2 or 3 left and it gives you no indication which ones you've done and which you haven't.
And I've only done about 8 of the unique jump stunts. :\
There's loads of other things like that where I've not really started (e.g. shooting lessons, hunting, flight school, races, bail bonds, smuggling, yoga, ).
I'm hoping (but not optimistic) that at some point it gives you some help with the collectibles. It'd be nice if it flagged the remainder up on your map once you've got 75%, or something like that.
Favourite characters in the game (so far) by the way - Nigel and Mrs Thornhill.
