When I did w2s, I started timing it from when she was asleep - I'd be shhh/patting til she was asleep, and then knew it would take about 20 min for her to get into deep sleep, so I'd wait 20 min, go in, tug on her swaddle or scooch her a bit in the bed. W2s can be a bit tricky, so what I'd suggest is going in at maybe 15 min and just watching what happens as he wakes up - and what time he starts doing what - that can help you learn the signs of his waking and intervene before he wakes up totally.
If you cannot extend his nap (and I'd only try for 20-30 min), then I'd get him up, if he's hungry, feed him right away (if he's crying while you're extending the nap, he may very well be hungry earlier than 3 hrs), and only give 30 min of A time after the feed, max before you put him back down again. If you can extend the nap, let him sleep - I wouldn't let him sleep past the 3 hr feed mark - at this age, he's still so very young and your milk supply is still being established.
In terms of a small feed before bed - isn't that what you're doing with your 2nd cluster feed? I bf my dd before bedtime from birth til a year when she weaned that feed. As long as you're putting him in the crib somewhat awake, it's fine. If you find he always falls asleep during that feed, then after the feed, change his diaper, swaddle him, and do your regular wind down routine - that will wake him enough so that he doesn't associate the feeding with the sleeping - you just want some space between the two. BFing is very relaxing for bubs, and bm actually has a hormone that makes them sleepy, so it's pretty common for bubs to fall asleep while bfing - so when my dd was really little, after feeding, I'd change her diaper, put her in her sleep sack (or swaddle), we'd pray, sing, and into bed (our regular wind down), and that would usually stir her enough to be awake when she went into bed.
Have you decided to continue or not with the rice cereal?
hth
michelle