Been thinking about this post off & on since I last replied. I need to be a bit more emphatic.
I would absolutely shoot slugs for practice & the more the better. & the more variety regards distance, conditions, ranges, etc.
That SG o' yers can be employed very nicely as a "short-range" rifle with impressive capabilities. That it'll do shot is a big plus - or visa versa.
I would suggest though that you'd buy a few 5-packs of slugs, stick the SG on sand bags & see what shoots best - accuracy-wise & then stock up. You don't need the high-dollar/hi-po slugs as anything you can hit with will do the job. Try the less expensive first & work up till you find what shoots good & then buy a bunch - stock up best you can.
Too, it may be that you'll need to go through some tweaking to get more used to a bit stouter load - fit, etc. or maybe just more shooting to get more familiar if a new-comer to shotguns. There's no "shame" in getting yer butt kicked by stout loads in a SG (we all have), but you don't really have to put up with it - there's answers here.
The advise about not killing yourself at the range is good. Maybe only 10 or so a session & maybe those low-recoils you have work just fine - all the better.
Paper targets can be just fine if you work them into somewhat of a drill. Quick target acquistion, double tap, reload do overs, etc. Work up to it, & maybe using bird shot till you're getting on the target more regularly, then towards the slugs.
Better than low-recoil slugs though, are ones that hit where you're aiming & every shotgun is different. Do use those that hit where you aim.
I ran across some 12 gauge PMC Brennekes for $1.99/5 pack locally - 1 0z at 1600 fps & shoot like a dream in all my 12s - I bought a bunch & they're not too bad re recoil. Look 'em up & try a few.
Alas, none to be had in 20 ga & the "real" Brennekes are $2.89/5 pack here ... wah!
Wanna wring out all the bennies of having a shotgun - ya gotta shoot slugs.