I always like to hear of folks wanting to get into R2R!
Why do you want to? To record? To playback an existing library of tapes? To subscribe the The Tape Project? Your motivation makes a big difference as to what deck(s) to seek.
What media do you currently have and/or want?
The best quality media, currently available is 2 channel dubs of master tapes recorded for playback at 15 IPS. The Tape Project is obviously best known here! (I have none ;-( !!)
IMO, the best commercially recorded tapes are 2 track 7.5 IPS.
The greatest selection of titles is 4 track 7.5 IPS.
Many early rock recordings were done 4 track 3 3/4 IPS,some sound alright, but the only choice for some titles.
A deck must have playback heads for each format. Again your media dictates. I use Otari MX5050's with switchable 2 and 4 track heads, because I have both formats. I also have a Teac SX4300 that plays only 4 tract but has auto-reverse for convenience. Casual background music, the Teac. ) lately, more the Squeezebox) Serious listening session... the Otari.
What makes a deck a "pro"? Manufacturers' targeted market. Built like tanks, few "bells and whistles" built to be simple. Reliable, modular, studio serviceable. (Ampex, Studer, etc.) Next would be prosumer such as Otari and Tascam. High build quality, better quality parts, serviceable. Consumer decks are just that. Not necessarily bad, but usually trading "bells and whistle" for sound quality and reliability.
Sansui SD7000...Why? "HiFi" is marketing, nothing else.
Hope this helps. Would be great to have another R2R fan! I love my R2R's and have a decent sized library of 2 & 4 tract tapes. I use a BottleHead Seduction for direct from head playback. I bypass the solid state amp boards on the Otaris. Now that is "HiFi" with substance!!
Cheers,