Help in putting together my system with used equipment on Audiogon and eBay.

Have you checked out Kef, ADS or PSB loudspeakers? I know they are old school but they sound good. New KEF is not cheap but they have amazing towers that are full range. I own ADS and if you get the flagship tower model it will give you all the bass and sweet highs you would ever want. Unfortunately some of these brands are getting old and hard to find in good shape. Good luck!

I will be 65 this year and after many years of rock concerts my ears are in great shape, but I am very careful with listening volume these days. I also for many, many years had integrated amps, both solid state and tube. Several years ago I went to separates and am so glad I did. I know there are integrateds that rival separates, but you can’t customize your sound as easily, and you have flexibility to try combinations of tube and ss components. Personally if your main source is digital I would put tubes somewhere in the system. They add a richness, fullness and naturalness to music and vocals. I also have a pair of used EgglestonWorks Fontaine Signature speakers from a fellow Agoner on a great deal. I would look into Spendors also. Have fun putting your system together. It is a great hobby!! Just my thoughts if I were starting from your point. 

You can do much better than B&W, whose reputation is the result of massive advertising rather than real merit.  

@ the OP. With your permission and after re reading your initial post I’m going to dare further trying to help.

Pass Labs X1 Preamp, my rock to start with

Excellent preamp but conceptually speaking and unless you have a preference for solid state and IME and other members on this forum you could follow the hybrid approach and match a tube preamp with any amp tube or solid state, the recommendation for an integrated also valid if budget is a constraint and you want to keep it simple. But IMO I would go tube preamp.

Bryston 4B SST

You said it plenty of power is best than limited power, quality matters too but in your case the Bryston is solid and good, if you like SS well Pass is amazing but at a higher cost.IIMO you can keep the Bryston for now

Do I need a DAC?

Oh yes you do, not a used old one, with DACs you need to keep up with the latest iterations, it is hard to find good used recent dacs in the used market and the price is sometimes more than what you will pay new. You don’t have to spend much on a good dac. The DAC subject IMO depends on the pre used, let me go a step back, you would want to use balanced interconnects whenever possible, not saying single ended is bad but if your equipment supports balanced then your DAC should support balanced as well. With dacs the power source is essential, good engineered dacs will work well with their stock power source, others good dacs which are cost effective will benefit from a good linear power supply, doesn’t mean the DAC is not well engineered just that to keep it cost effective the manufacturer couldn’t not supply the DAC with the best power, good transformers, EMI shielding, caps etc are expensive.

Phono. I’ve realized that might be a big reason why people go to separates isn’t it? I’d like to hear some comments on this. If you have separates and no phono, what do you use? Stream music? CD’s?

TT are great but you need extra budget and vinyl for this which you don’t have, I thinkyyou are better off streaming music, qobuz had a decreased pricing on their subscription model cheaper than Tidal better quality, Tidal is good too. You could stream from a PC to the DAC, I could provide you with more details if you are interested.

but I know which albums I would buy so it is an option. I wouldn’t know a good phono if you hit me with it. Please recommend a few.

Good phonos are pieces of engineering, it will get expensive, not only the phono but the phono power supply, tonearm and cartridge, then the adjustment, then a good pre with phono stage, if you have the money absolutely if you are on a budget keep it digital or CD. BTW vinyl can be cheap but remember does cheap vinyl releases most of the time were created from sub digital recordings, if you like pink Floyd for example what you are getting with the latest pressings is not the original quality but digital mixes which have lost resolution, I have some English 3rd releases of pink Floyd and it gets expensive (and old so little scratch could be an issue), the sound is amazing better than digital IMO but at a higher cost. Some companies are collecting the original masters and creating vinyl presses from it (mofi) and these are better than the $15 releases but be ready to pay $40 to $70 or more. BTW the Florida expo have excellent vinyl setups if you are interested, there is a dealer in Deland which is an exhibitor and have 2 vinyl rooms there, he plays new vinyl from masters with different speakers, cartridges even mono (which sounds great) and he is a great person, very helpful, he has a cost effective room and a more upscaled one, his name is David http://www.alc-pro.com/

You all have heard more speakers than I ever have and will
but I want them to be used and costing much more when bought new.

Well if you attend the expo you will have a chance to hear many speakers and then you can buy these used after if you want. Some speakers will be discounted and if you shop around you might even get a floor sample but like you said the used market will be cheaper, this is really a personal thing.

Apologies for the long reply hope it helps.

Just noticed @moofoo reply, +1 I share his opinion on tubes and separates completely.