1 = main meepo
2 = all other meepos
3 = 2&3 meepo
4 = 4&5 meepo
I haven't quite gotten the hang of making the most of my first extra meepo (like keeping one in lane and jungling with one to max out exp/farm) but once you start to get 3-5 it's pretty easy to keep them split up farming separate jungle camps while one is in lane or roaming around with the team to start fights.
I've been meaning to try quick cast with Meepo, but I've gotten pretty good at tabbing thru them all and tab-W-click'ing with them all pretty quick.
I don't have any profound tips for fighting with him other than practice tab-netting spaced out enough so that they don't overlap too much and poof spamming. I'm still practicing with blink poofing which is selecting all other meepos, poofing them to the main meepo, then switching to the main meepo and blinking onto an unaware target right as they all go off. I've been mostly relying on blinking into range, netting a dude, then just walking over to him with the initial meepo while the others poof onto him.
People I group with say I shouldn't get the Mek and that I should let supports handle that, but I find it WAY too useful for farming and I like being the one that can control when I use it in a fight if I need to desperately save one of my meeps from certain doom. It's probably a crutch tho and I probably won't need it if/when I ever get actually good on the hero.
Still, nothing is more fun than surrounding and overwhelming someone with a BKB on with geostrikes. There aren't many heroes that will walk away from a 1v1 engagement with Meepo. He's a really fun hero.