I've been there. Made additional trips to store to get more valves/couplings/pipe because I couldn't get a valve to sweat.
Sweating in cheap china-brass valves can be a real pain. Far more difficult than sweating copper fittings. Add to the challenge, you can't get the valve too hot before you melt out the nylon sleeve. It's almost like the cheap brass is self lubricating and has oil/crud in the material. Ironically a really hot pinpoint torch helps so you can get the joint hot before overheating the adjoining pipe/valve.
It's always good to keep a few sharkbite caps around if you need to cap off a branch/project like this and get the house back online.
I kept a few "better" brass valves around until my recent pex repipe. That said, I sweated all my copper to pex transitions (no pro press) including the incoming 3/4" main line but I purposely avoided brass fittings, using ONLY copper transition fittings instead. Partly due to ease of sweating, but also because "lead free" brass isn't really "lead free", or arsenic free, or bismuth free...
My local supply house will rent the pro-press tool for $75 a day (some plumbers don't have them) and they carry all the fittings. Far less sensitive to cleaning/fluxing, no heat, no scorching nearby wood, faster, no need to get the line completely dry. There are many upsides to going that route that overcome the additional cost of the fittings. As much as I see it used, I assume the rubber o-rings are resilient enough to not fail before the copper.