Just getting back to DW

Welcome back Coral.
(Great, now I always hear Rick Grimes when I read your name... )

I can only advice to go for RA. There's little reason not to play with it, as DW vanilla is simply lacking in all departments.

You can play all old missions with RA, except FFG missions, as RA basically created a new class, which renders the mission unplayable - but this can be easily edited/fixed in the editor if needed.

All others work and are generally compatible.
However, some missions are hit and miss, as the sensors get changed drastically from vanilla, which can cause problems, but mostly, it won't.

The missions provided by RA, as Wildcat mentioned, are rather crap.
The problem is, the Russians don't do any quality assurance, nor do they seem to give a damn about immersion, as every briefing from them is cluttered with typos or grammatical errors, because they use google translate AFAIK.
Now, one exception is the Red Storm Rising campaign, it comes with RA - but has to be installed seperately (for whatever reason?). The file is in your missions folder, you'll see it.

RSR by Bill Nichols is the best campaign available for DW in my opinion, and adds something to the game, the developers overlooked: Immersion.