There are 2 sides to this.
1. All green lanes in the UK should be fairly easy to drive. They are roads at the end of the day. If they are really challenging, then you might not be on the lane.
2. Having said the above, you are in the middle of nowhere. So go prepared. Should you get stuck or stranded it is a long way to go and get help.
Considering the above. Have you done many lanes before? Normally it is worth going with at least one other vehicle. Solo laning is fine, but obviously comes with much higher risk should something go wrong. Including just breaking down. Phone signal is normally rubbish in these areas. So you'll have to be up for a long walk. And Strata Florida is in a particularly un-populated area.
There are lots and lots of other lanes in Wales, you may want to consider them instead or as well as. Strata Florida is quite long, the constant jolting and bumping over the rocks can wear on you if its getting late.
Make sure to stay on piste. Straying from the legal byway is illegal and only helps to get lanes closed to motor vehicles. Highly advisable to use a mapping tool. You can get some really good apps on a smart phone where you can download an OS map and track & record you live location, while showing where the by-way actually is.
As for the Strata Florida, its pretty standard for a Welsh mountain lanes. Not really all that difficult, not really a challenge in an off road sense. A few bumps and lumps. There is quite a bit of water and some deep water crossings. These pose a genuine risk if the water is high and/or fast flowing. Plus deep water wading can always take a toll on any vehicle. Most times it should be fine, but it could cause alternator, starter motor issues etc.
