I'm a bit late to game in this forum, just started with the MiSTer project but some notes with regard to soldering the SDRAM board. I've done a lot of soldering over the years. I also have a reflow over, hot air station and of course a hand iron. I've built 5 RAM boards (for myself and friends) and consistently get 160+ with Alliance RAM.
1. First I suggest using Alliance memory, getting cheap or NOS memory on eBay will most likely end if grief. Don't panic about not achieving 160+mHz in a memory test, 150mhz is sufficient. I suspect 99%+ of the cores can't go that high anyway. A typical fMax on DE10-Nano boards with the T80 core (used for most of the arcade cores that require a Z80) is probably around 150-155 and that's on a good day... Probably more like 130-135mhz is to be expected. In other words if you can pass at least a 150mhz test then you are fine. In fact you are probably OK with on 140mhz.
2. Any SMD 0805 package capacitor in the range of 0.1uf - 1.0uf will work. That is, you don't need to get the "exact" Kemet part.
3. No need to go overboard and use a stencil with solder paste and a reflow oven (unless you have one of course). However, I suspect if you have a reflow oven you don't need my advice
. The chip can easily be hand soldered even if you are new to soldering.
4. I suggest soldering the RAM using a "drag solder" technique and plenty of liquid flux (there are probably plenty of Youtube videos on this). There is no need to solder pin by pin, besides it will take forever. Drag soldering takes seconds. For SMD hand soldering, I use Kester 959T Soldering Flux and Kester 32117 Solder (1.57mm) with a small chisel tip. I've tried many types of solder over the years and I've found that Kester is the best. Secure opposite corners of the ram with solder, apply lots of flux to the pins (but don't go overboard), apply solder to a clean tip then drag it across the pins. Repeat 1 or 2 times as needed. Apply a little bit more flux to clean up any bridges with iron. Should take only a couple of passes and it's quick and effective. Inspect with a 10x loupe or microscope. Note: High quality solder and flux is a must! Do not use cheap solder! If soldering by hand I suggest using 60/40 tin/lead solder (unless you are environmentally conscience, but lead-free soldering can be tricky)
5. Remove flux and debris afterward. Although there are differing views on this, RAM can be sensitive to stray capacitance and certain fluxes can cause problems in this area (I find I get better performance after cleaning the board). Note: you do not need to buy specific "Flux Remover". I use Isopropyl alcohol (ethanol or methanol work fine as well) in a high concentration (around 90%) and a soft-bristle toothbrush. This can be purchased easily in a pharmacy (chemist). I usually rinse the board immediately afterward with demineralized, distilled water but this is probably not necessary. Do not rinse the board with tap water!
5. Again, inspect the solder around the pins using 5-10x magnification to look for: not enough solder, too much solder and most importantly solder bridges. Also make sure there are no debris around the pins (especially fine copper wire if you used a solder braid to clean up excess solder).