I like Milner and wouldn't mind him as a cheap utility player. Could take the place of Rosicky/Flamini and fill in a number of positions. I couldn't see regular games for him though and I imagine he would be a bit pricey for that sort of role.
Cech would be my dream signing. Still one of the top keepers in the world and should still be playing at a big club. But Mourinho wouldn't sell to Wenger and United are likely going to be in the market for a keeper this summer so I wouldn't get any hopes up on that front.
Milner would be on a free so would be wages demands only to navigate. United may need a keeper but with a decent backup in Valdez, I can't see them going for an older keeper like Cech.
On the contrary I would expect United to be all over him if he's allowed to leave, assuming De Gea is off. He's still around the peak age for a top level keeper. He could give them 5 or 6 great years like Van Der Sar did (who was 3 years older when they signed him).
Didn't realise Milner was free. Still think his wage demands would be too high for the place he would have in the squad.