You do not have to do market orders, and on coinbase there is no fee, as long as you set limited orders.
Furthermore, what does it matter very much about which exchange, whichever one you can get onto and then of course your spreads would be farther apart if there is a higher fee in order to at least cover the fee.
I agree that you might be inspired to move some of your trading based on lower fees, which I did when I moved some of my trading from Gemini to Binance - but each exchange has its plusses and minuses - and even questions about whether you are ready, willing and able to link a bank account to the exchange, which options would likely depend somewhat on your origin country, too.
Coinbase has NO spread because of the way the fee structure incentivises bots to be market makers. The bots are some of the best I've seen, best in the world bots..
I like to place market maker trades myself because I like to trade inbetween walls, and the bots there are just too much competition for my trading style. It doesn't feel good..
I like to be on the high volume exchanges where that exchange is making the world market, or atleast have a close eye on those charts too.. Always watching a few..
I usually take a LOT of tiny stoplosses too so low fees make it a lot easier to get back out of a trade I no longer like the look of.. Which is incredibly hard to do on coinbase trying to get in with those bots..
I made a binance account for the first time last week when I was chatting with some group trading there, where I found that tool you all like so much actually, but I decided that I really didn't like the new shitcoins of the day trading there much and the group turned out to be really just trying to sell TA to pretty much puppets that would trade their TA..
I have a hooked up coinbase but I don't figure I'll need my bank account UNLESS I DO AWESOME TRADING!!
And about exchanges with no margin.. Then I can only make more BTCs when the price is going down..
If I have margin I can also make more BTCs while the price is going up! And down..
I'm checking out the usdt/btc on binance right now..
I might have crypto trader PTSD or something < made that up..
I really want back in there but I just haven't been able to bring myself to do it.. Probably causing my exchange indecision..
Whatever you are describing yourself as doing in terms of BTC trading and preferences seems strange and disjointed to me, even though I understand that each person (assuming that you are a person) has a different approach to trading or accumulating bitcoin and goals, and each person has a past practice of employing differing strategies in terms of the extent to which they gamble their whole trading stash or if they are content with trading smaller portions of their stash (whether attempting to accumulate fiat or BTC).
So, yeah, I get it that you are attempting to trade rather than purely accumulate bitcoin and HODL, and you seem to want to trade BTC in order to become profitable whether you measure your profits in dollars or in bitcoin remains unclear to me because you are not describing whether you have connections to banks or how you might have planned to cash into fiat if that was one of your goals. Furthermore, it sounds as if you want to attempt to profit from smaller increments of trades, but you do not have bots yourself, but you believe that you are not able to profit as much if you conclude that the bots are more prevalent on any given exchange?
I personally believe that you can still profit if bots are present and if spreads are close because the main way to make money is to bet based on the movement of the price rather than the spread.. because when the BTC price moves, it seems to move on all exchanges in the same direction, and sure of course some exchanges will move faster and further than others, but there also does not seem to be much of a pattern for well established exchanges regarding which one is going to move farther or moves first. So, in that regard, it can be useful to have some value on more than one exchange, and sometimes even if you set orders at the same prices, the orders might sometimes fill on exchange A more often than exchange B, but then that situation can reverse, from time to time, too.
It appears to me that whatever you are attempting to do falls into a category of kind of winging it, and unclear to me how what you are doing is not just placing a bet and then gambling that the BTC price moves in that direction and then if the price moves in the opposite direction then you replace your bet by another bet, and so ultimately you are hoping to gain profits (but you are kind of expecting to NOT have any money left (principle or profits) after going through the process for a while and that is why you have not set up any exchange accounts that are linked to bank accounts)?
Personally, I believe that it is much better to attempt to establish your initial trading stash without margin and to get a hang of the situation, but I understand that you can gain a lot more by use of margin, if you are lucky (or insider information) enough to be able to place your bets in the right direction.
Also, it appears that every single shitcoin that forked off of Bitcoin core 14.0-16.3 is also going to have to patch things up. We really dodged a bullet here. Hope no other surprises are lurking in the code. 
