1. Ya, that sounds like a good little set up to get you going. I like the Project DS with the 2 tubes. IMO< the PreAmp/Amp are the heart and soul of a system. And the Project DS@ allows you 2 12AX7 tubes to play with. The tubes can also tame the high frequencies of the JBLs if needed. (my ears are sensitive to horn tweeters, these have a dome tweeter with some horn design/tech. the horn design can be too piercing to me. but with tubes, you should be ok if that happens.
I also like the options on the DS2 and the JBL speakers. eg. subsonic filter, gain/capacitance options, options on the JBL for near field listening if the speakers are near the wall or on table, etc. Those little tweaks, used all together, will allow you to focus on a sound you like.
2. I generally recommend for someone starting out in this hobby to stay with the same brands if possible from source to pre/amp to speakers. But you don't have to. If you decide to mix brands, you have to just make sure the brands electronics work with each other well. e.g, impedance matching, gain matching.
But if you decide not to go with the Project TT, IMO, that is fine, just do a little bit more search. There are many good entry level TTs out that at the same price point as the Project Debut. But, if you wouldn't mind, I would be curious to see the reviews that say the Debut hums, and the phono stage that they used with it. B/c, as we've talked about, the audio pieces need to match electronically, and for that, we need to look at the specs.
3. here is a link to Audio Advisor, an online store that I buy from sometimes. they have good prices for entry and mid-budget TTs.
https://www.audioadvisor.com/products.asp?dept=78#/sort:ss_price_min:asc
Rega are good. the Marantz is prolly good. NAD prolly good. But I really like Music Hall- Big Bang for buck. Designed in the US, and I think made in US too (but not sure). The owner of Music Hall is known for quality at affordable pricing.
other link for my "go-to" website for general info:
https://www.musicdirect.com/equipment/turntables/?category=Turntables&sort=sitePrice|ASC&page=1&pagesize=24&c1=tab-products&c2=grid
they often have great deals on sale or clearance.