As a rough ballpark figure, you're likely to see trailing at around 400 / focal length seconds or longer. Adding a 2x barlow doubles the effective focal length, and thus halves your longest usable exposure (It also gives you 1/4 the photons/pixel for extended objects, so generally not a great idea for AP on a non tracking mount).
Yes, you can combine a lot more pictures - I've seen a nice photo of andromeda that someone took with a camera and 300mm lens on a normal tripod, by stacking hundreds of around 1 second exposures. But it's a LOT easier with a tracking mount. (For more details of the tripod only approach, see Forest Tanaka's video at
You could see if there's an add on motor available for your equatorial mount - they're usually more for visual use, so may not be as accurate as a motorised mount designed for imaging, but should at least let you go to somewhat longer exposures.
If you want to get seriously into deep sky object imaging, you're going to need a decent motorised equatorial mount.
Alt-az goto mounts suffer from an effect called field rotation, where the field of view gradually rotates as the mount tracks an object. This limits you to around a 30 second max exposure before you get obvious trailing from the rotation (it varies with latitude and where you're pointing).
Equatorial mounts don't have that problem, but you'll still need a good quality one - for imaging, you want to keep the image in the same position to a pixel-perfect level. For visual use, you just need to keep the object somewhere in the field of view.
As a rule of thumb, if an equatorial mount doesn't have autoguider inputs, it's likely not going to be accurate enough for long exposure imaging. Also, try not to exceed around 50% of the mount's rated weight capacity when imaging - the capacities are usually quoted for visual use, which isn't as demanding.