N is standard weight and I believe NH is heavyweight. I believe one can convert from one to the other with the correct parts. Yours is most likely the N version.
The 5410 has an oil pump that lubricates during sewing. If you sew slow you might want to think about running full speed without thread or needle and presser feet lifted for a few minutes at the beginning of every sewing session to get the oil through the machine.
For myog creations, it is either bonded polyester or bonded nylon. I get mine at wawak.com (Amann brand: serabond and strongbond). V69/T70 (two ways of identifying same thread) would be where I would start. Guys with triple/unison feed machines can use up to T135 thread.
Most guys prefer bonded nylon. I tend towards bonded polyester.
Thread sizes chart
Bonded nylon or polyester thread specifications chart with corresponding minimum needle sizes
www.tolindsewmach.com
Link for thread and needle size (it is a pdf download)
Shop for Amann Strongbond Nylon Bonded Thread. Tex 70. Great for heavy-duty seams. Ideal for handbags, leather goods, and shoes. Free shipping on orders of $99+, order from WAWAK today!
www.wawak.com
Based on above link, if you use T70 bonded nylon, it is recommended size 18 through 21 needles.
Sewing webbing loops
Sewn loops on webbing are used in a variety of load bearing applications.
www.sailrite.com
You would want to ensure the machine is properly setup/timed. You can take to a sewing machine mechanic or find a service manual and do it yourself.
Enjoy!