Ok, so for chain-grabs it goes like this:
about 50% you can chain-grab fast-fallers. I only really get this down easy on Fox, as I play against that character more than Falco or C. Falcon. Usually when I go against those two I just U-throw to an attack instead of grabbing again, unless I see they don't DI, then I just grab, shock, and U-throw to get a DI and hit 'em.
However, when Fox DI's behind me I notice I miss him a lot, I haven't checked on AR if it's impossible to chain-grab him with a good DI backwards, but I'm pretty sure it is, I just don't expect it and usually just go for an attack anyway.
About 120% is when he can jump out of it or something and at that point I will N-air him to his death or an edge-guard.
Tech Chasing is usually easier.
Also, Grab resets are good. When I know I can't chain a grab, I will D-tilt and reset them so they're standing on the ground not knowing what's going on and I grab 'em again and U-throw and check the DI for a chain or a combo.
Usually I follow up an U-throw with a F-air to U-air to N-air/B-air/D-air to get them off the stage and rack up a bit of damage (on both of us, haha)
On bigger, heavier characters you can probably get a F-throw chaingrab on them, but good players will probably know to DI away and hit you with a fast attack (like Bowser's Whirling Fortress, the Up+B). But I have successfully chained F-throws on them and frustrated them that much, after about 5 throws like that U-throw into a combo and edge-guard from there.
F-throws work like a charm against walls like the tree in Pokemon Stadium (counterpick!) After they get to about 50% U-throw/d-throw to an U-Smash and Thunder, Pichu is too good. That is the Chain Lighting Chain Grab (as I showed in my Chain Lightning video on Peach on Peach's Castle).
D-throws are good for tech chases. I usually run to where they'll go and U-smash, although a D-smash could be useful at the edge. I've been working on getting the Agility (Up+B) to the frame to see if I could get that work with tech chases.
That's all I can think of right now.