1. It looks like the consumer version of Vega will release around August 3, but keep in mind what past AMD flagship releases have been like; there's almost no way that you'll be able to buy 5 of them on Day 1, or even in the 1st month, tbh. No one really knows what Vega will be like as far as its mining capabilities are concerned; it will probably be awesome, but there's no telling what the price will be like, and if it is an incredible miner, expect them to be sold out constantly for at least 6 months, with prices at a premium above msrp when they are available.
The biggest consideration here, however, is why you are mining; if you're interested in making profit, then everyday you wait is a day that you're LOSING money. Generally, the best way to go if you're looking to mine with AMD is to buy all the RX 480's you can and just GET STARTED. Mining ETH, an RX 480 @ $250 should pay for itself BEFORE the new Vega cards even come out! You can use the profits from your RX 480's to BUY the Vega cards if you want (^_^)!
A lot of people have tested the RX 480 vs RX 580 and found that the hashrate is nearly the same, but that the 580 uses more electricity for some reason. If the RX 480's are unavailable or are just being priced too high for some reason, RX 580's are a good substitute, and will also pay for themselves BEFORE Vega even comes out.
If you want to go high-end, however, you can always consider Nvidia; I take absolutely no sides on the Green v Red debates, I own cards from both companies right now. AMD gets much better ROI on ETH, but right now I'm getting more than a LOT more profit/day from Nvidia (1070/1080). Here's an example of what kind of performance I'm getting from my GTX 1080's using CCminer 2.0:
https://whattomine.com/coins?utf8=%E2%9C%93ð=true&factor%5Beth_hr%5D=28.5&factor%5Beth_p%5D=105.0&grof=true&factor%5Bgro_hr%5D=92.0&factor%5Bgro_p%5D=130.0&x11gf=true&factor%5Bx11g_hr%5D=12.5&factor%5Bx11g_p%5D=120.0&cn=true&factor%5Bcn_hr%5D=500.0&factor%5Bcn_p%5D=100.0&eq=true&factor%5Beq_hr%5D=465.0&factor%5Beq_p%5D=120.0&lre=true&factor%5Blrev2_hr%5D=48500.0&factor%5Blrev2_p%5D=130.0&ns=true&factor%5Bns_hr%5D=1050.0&factor%5Bns_p%5D=155.0&lbry=true&factor%5Blbry_hr%5D=387.0&factor%5Blbry_p%5D=120.0&bk2bf=true&factor%5Bbk2b_hr%5D=1600.0&factor%5Bbk2b_p%5D=120.0&bk14=true&factor%5Bbk14_hr%5D=2500.0&factor%5Bbk14_p%5D=125.0&pas=true&factor%5Bpas_hr%5D=940.0&factor%5Bpas_p%5D=120.0&bkv=true&factor%5Bbkv_hr%5D=0.0&factor%5Bbkv_p%5D=0.0&factor%5Bcost%5D=0.1&sort=Profitability24&volume=0&revenue=24h&factor%5Bexchanges%5D%5B%5D=&factor%5Bexchanges%5D%5B%5D=bittrex&factor%5Bexchanges%5D%5B%5D=poloniex&dataset=Main&commit=Calculate&adapt_q_280x=3&adapt_q_380=0&adapt_q_fury=2&adapt_q_470=3&adapt_q_480=2&adapt_q_750Ti=0&adapt_q_10606=0&adapt_q_1070=1The estimates that whattomine.com uses for the 1070 are almost 1/2 of what I'm getting for Groestl, and about 30-50% lower on LBRY, or Lyra2Rev2. But if sticking w/ AMD, which is better ROI for Ethereum specifically (a currency that's going through the roof lately), Just grab some 470/480/570/580's and get started, definitely do not wait for Vega! You can always sell those cards later to buy Vega, or just put together a new, all Vega system and SCALE UP!
2. It still looks like Ethereum (ETH) is the way to go w/ AMD. Ethereum mining is getting harder, of course, and they're planning at some indeterminate date in the future to switch to a PoS system instead of PoW, but if you're willing to HODL! for just a bit longer, Ethereum prices just seem to be going up & up, and while we all thought that the cries of "ETH is the next $1,000 currency" seemed like hyperbole a few weeks ago, it doesn't seem like an exaggeration anymore...
ZCash is by no means a bad currency, however. You could always just mine both of them at the same time, if you want to hedge your bets.
3. Probably. Nobody knows yet, but... I don't see why not right now.
4. For AMD, yes. Especially with a card that's been out for a while, like the 280x or 390x, people have had plenty of time to get the BIOS mods fixed, and then fixed again. For Nvidia cards, it gets a bit more sketchy, especially with newer cards; on the 10xx series, BIOS mods have to be "Signed", which makes the whole process slower and more difficult, which is why you don't see many mods for it.
If BIOS Mods make you nervous, though, you can get most of the performance you would get out of it from a simple overclock/underclock procedure in Afterburner. BIOS mods are really for squeezing that last $0.05/day out of each cards, you won't see "10x THE PERFORMANCE PER CARD!!!" from it or anything.
