I would say go with a istick 50 watt, and a kanger mini sub tank.which is my go to.
But you definitely want a mod that takes two 18650 bats, Not one!
1 bat might only get you 4 to 6 hours of vape time with 2 bats guaranteed at least 12 hours.
Then all good with a one bat mod.
Even if you don't use the wattage, having a dual battery mod is great for battery life. I get about 1.5 days of pretty heavy use on my Sigelei 150, running about 50/50 between 30w-ish with an RDA and 15-ish on my subtank
temp control is nice to have if you ever want to use it although at the price point it worth it just for 100w mod....
Ipv4 may be an option temp control, 100w... Latest in terms of vapor tech imo. Remember, 100w device can also do 50w
I also seen a CHEAP 50w recently, don't know anything about it tho. The Smowell dpv-50 $27 from gearbeast. Also devices like the zna 50w clone (original was only 30w). Kbox is cheap too 40w mod like $20 but there's only a handful of preset wattage choices between the min w-40w
Fasttech has the dvp for $31 I think. I haven't used gearbeast but don't mind ordering things from China, if I can wait
I'm experimenting with a new Chinese supplier that seems to be bending over backwards to try to get some new customers, and seems willing to stock whatever they're assured there's a market for - hit/miss on the pricing, but when it hits it's out of the park...will hopefully know within a week whether they can deliver on promises, ordered Saturday and shipped Monday...
Which supplier?
All these people are saying is we understand your thinking of not needing much in the beginning but I would also strongly recommend getting something like the Segelei 100 watt plus if you're thinking 50 watt box now anyways....with the dual batteries and keeping it turned down to 50 watts or below you'll get good run time off of it and that one day you get curious down the road of what it's like to crack it up you don't have to spend double the money to find out...That being said, I also recommend you purchase a back up device in the near future as accidents can happen and the last thing you want is to be caught without a vape. So, IMHO, I would go for something like the 100 watt plus and then a little ways down the road grab something on the more economical side like a 50 watt Istick so you're prepared, you have a backup, and you have all the power you'll ever need to keep you vape happy. Vaping above 100 watts is pretty much pure self indulgent cloud chasing anyways...I have yet to vape a liquid I thought tastes better over a hundred watts than under and usually the flavor I get is dry wick from forgetting to drip between hits 
