If you like to do Astrophotography and only occasional observation, I strongly suggest you don't buy any telescope at this time.
Your mentioned camera is more than adequate for now.
Your 55-250 is fantastic for very many wide angle astro subject photography at night.
Only for now, you need to start strong study of the subject and there is no such thing better than joining your local and nearby star club. You can find the address by yahoo search.
Download (The free) following softwares and get familial with
Stellarium,
DeepskyStacker DSS
,
RegiStax.
Next step could be buying a good and light sky tracker. With your current tools or may be after adding a Samyang/Rokinon 14mm F2.8, you would be able to get the most beautiful images of the milky way and night landscape, with your 55-250, you can have excellent images of the Andromeda, Orion or likewise to start. That is as you also learn about your sky and constellation, then equally importantly, post processing. You also need a cheap cable release such as This
or likewise.
I recommend iOptron 3302 SkyTracker
, assuming you already have an above average camera tripod Mount.
If you need to invest more heavily (as first step), you may want to look into
THIS
Feel free to upload your images down the line, even the "Bad" ones, here for advise and I can tell you will get some very good ones. If you want, you can join a dedicated astro online site such as "Cloudynights"
, but you may get kind of advise that fell high above head with less tolerance to novice user photographers there compare to what you get here.
For observation only; & for now, your best bet is to buy a good astro grade bino that doesn't break your bank such as this one:
Celestron - SkyMaster 20x80 Binoculars
with this tripod - LINK
If you already have a 7x50 or better 10x50 binocular, that might be adequate too (Wide view).
It will be very clear to you in no time to figure out if that is the right time to go farther and open your wallet even more, without regretting later. Your hard earned $ needs and deserve the utmost respect. Don't lose it on impulsive actions.
May your skies be cloudless and dark.