What I'm looking for is something reliable (aren't we all?), reasonable accuracy at 100-300 yards, the ability to mount optics and hopefully something not too expensive to buy extra parts, accessories and magazines for.
Also can anybody give me a general sense of the size and weight constraints of each rifle? ]
I don't plan on hunting with the rifle just a lot of target practice. As for NR vs Restricted I would prefer NR but its not a deal-breaker for me as I eventually plan on adding a handgun to the system.
Are you planning on competitions with this rifle or just personal practice for competence/fun?
Regarding the highlighted sections in your quote, I believe a compact AR (like a 16" DDM4-V11 or perhaps a 10" DD-Mk18) would serve you well especially when the costs are factored in compared to a HK SL8, Tavor or an ACR as sweet as Onetwentyish's.
An AR should have a significant weight advantage on either of these fine rifles (meaning about a pound lighter which is significant).
Remember good optics don't come cheap, so factor in a good chunk of change for nice glass...
Your overall budget may be a factor (that's if you have one) as these rifles listed above (HKSL8, Tavor & ACR) are all close to $3,000 or more with tax before an optic is added.
Where as a very good quality AR will be under $2,000 leaving some extra cash for an optic and accessories.
Also since AR's are so popular parts/accessories/magazines are plentiful and they are arguably the most reliable/accurate and capable semi.-auto. Black rifle available today (they've had about 60 yrs. of R&D go into them and are in huge use just south of us).
While all these rifles are of high quality you will sacrifice accuracy with the Bullpup Tavor compared to the DD, ACR or HK-SL8; meaning it will be the only rifle of the bunch that is 2+ MOA, the rest should be capable of MOA or better with the right ammo./shooter/conditions...
Saying that a Tavor should be plenty accurate for banging 10" to 12" gongs all day at 300m and is easy to hold steady for non-supported shots due to it's design (rifles mass is closer to your body).
My recommendation if possible would be to at least handle/shoulder each rifle before deciding (especially the Tavor) and fire them too, if available.
Cheers D