1) Yes you will loose everything you sent, when you sent a coin to a wrong address. And yes, most exchanges have prevention to make sure you can not send BTC to an ETH address or similar. But as you mentioned, for BCH this is not possible since they are same format. But in some cases even this can be solved, don't ask me how (eg another exchange I saw has written at their deposit page that they charge 30EUR for restoring BCH sent to a BTC address).
But I doubt restoring coins is always possible.
So expect to loose everything, if you send coins to a wrong address -> tripple check every withdrawal!
2) A) "immediate or cancel" simply means, that your limit order is cancelled immediately, if it was not able to immediately fill your amount. Eg. wenn you place an order of 300 LSK at 0.001275, you only would buy 285.60 LSK and thats it. If you choose "good till cancelled" you will have your own "bid" in the orderbook for the rest amount, so a limit buy order o 14.4 LSK at 0.001275 and waiting for someone to fill it.
If you really immediately want 300 LSK at any price, you shold use a market order instead of a limit order. Then the missing 14.4 LSK are directly bought at 0.00127845.
2) B)
As mentioned above, you can make a market order, or set a higher limit price.
If you set a limit price of 0.00127999 for example, you would buy up to this price (but in case orderbook does not change meanwhile, you would still automatically buy first the 285.6 LSK at 0.00127500)
You can even place a limit order at 0.001274 and simply wait for someone else to fill your order.
2) C) See above.
You need to understand how an orderbook works:
You do not match a single order.
You simply tell the exchange what your max price is you are willing to pay, to get 2500LSK.
And then the engine is matching all the orders for you automatically, always getting the cheapest offer first of course.
So all you need to do is to place a limit order of 2500 LSK at 0.00128 and exchange will buy the cheapest coins available at the moment.
D) why are you always switching between USD and BTC price of LSK ?
Simply stick to one
(but I guess this is a beginner behaviour to always value something in fiat)
If you want to place a buy order cheaper than the actual market price, simply create a limit order at your price. Just forget about additional options. Normally you NEVER need "immediate or cancel". Just stick to the default settings.
You also do not need a "conditional" if you simply want to buy LSK at 5USD (assuming that 0.001275 BTC/LSK is valued ~5.5USD), just use the default settings.
(Explanation of conditioanl: This is also called "Stop Limit" and here you can say the exchange eg. "if price gets equal to/greater than 6USD, then buy x LSK at limitprice of yyy" If you leave out the limit price here, I think it will create a market order.)
E) first understand how an orderbook works, described above. Then you should be able to answer this question to yourself.
F) As mentioned above, just stop converting in USD or BTC all the time. Just use the price currency the exchange is offering you.
Yes it gets complicated when btc price moves and the result can be, that although you wanted to buy at 5USD, you bought cheaper/more expensive cause BTC price changed against the USD.
So easiest thing is just stopping to convert against USD and use BTC as it is. You do not say "I want to buy LSK at 5 USD/LSK" , but you say "I want to buy LSK at 0.002175 BTC/LSK". Some exchanges offer for some altcoins also trading against USD, there it is easier.
G) When you bought LSK and want to sell them at 6USD, then simply place a limit sell order at your price. Every setting is at default, no conditional nor anything.
Exchange is matching best offers automatically. If there is currently no one who offers 6USD or more for LSK, then your order will be added to the orderbook and you have to wait.
3) dont know what you want again with any USD value ..
4) Normally you can exchange your Tether at tether.io and bitfinex for USD (you need to verify there). But recently both had problems with their bank, so you need to imform yourself first, if they offer again withdrawals to bank account or not.
Bittrex itself treats tether like an altcoin, so not possible to do bank transfers there.
5) bittrex is no fiat exchange, so no bank transfer possible. You have to send your btc or tether or whatever coin to an exchange that has a fiat gateway. Eg. at Bitstamp (or coinbase/gemini as you mentioned) you can sell BTC for USD and then withdraw the USD to your bank.