UK in May/BritRail Pass Help Requested

The only way to know if a Britrail Pass is the way to go is to do the math. I start out by costing out all the train trips that I will be making. I use a number half way between the cheapest advance fare and same day peak time fare. Then I decided which pass I'm going to get. There is one that covers only Southwest England, one that covers all of England and one that covers all of the UK. It sounds like you would need the one that cover all of the UK. Then you have to choose whether you want consecutive days (unlikely unless all your train trips are one day after another) or a certain number of train days within a period of time (Flexpass). For example, we bought 8 days within a month. You will get a discount for anyone over 59. You will need to pick standard or first class (I always pick standard). Then see how much it will cost you and compare it to the fare calculation you did. I hope this makes sense and helps.

Edited to add: now that the actually routes for the days and times we will travel can be checked, I will be saving about £400 with my Britrail pass. This is because we don't do too many advanced fares because we really like the flexibility and convenience of the pass.

I was just doing this with someone last week, and started with the premise that Britrail was likely cheaper. They had a similar itinerary but three stops in Wales- Conwy, Shrewsbury and Fishguard.
You crunch your numbers, but I can say in their case even on the day fares worked out a good £100 cheaper.
I was surprised, and a good bit disappointed, as I was rooting for Britrail.
The thing to remember is that most, likely all, of these routes have cheap Advance Fares until minutes before travel.
So on Rick's rail charts you will see very high figures for on the day fares. In practice it is a!l but impossible to pay such fares. You can buy fixed cheap fares at almost a moment's notice.
I know you are both of an age for a Senior Railcard giving 1/3 off all fares all day outside London and the South East where it is after 9am, on a weekday.
However that costs £35 each.
Buy a Two Together Railcard for the same price, that covers both of you. But nationwide Monday to Friday is not valid before 9.30am.
So Senior Cards could be worth it, if you are early risers.
It was in the case above.
Looking at your itinerary I am 99% convinced, doing the maths in my head, that point to point works out cheaper by a country mile.
But please do your own maths check.

The best scenery in Scotland tends to be out in the west & central highlands whilst on the east side (Aberdeen) it is more like ordinary farmland - unless you go to Deeside (Ballater). I was really impressed by the Isle of Skye (which can be reached by a free road bridge) but it is quite a way out from Edinburgh and certainly not a day trip. Loch Ness is OK and very big but I thought the scenery was better in other areas - but don't tell the Americans as they are all at Loch Ness looking for monsters! If you are considering driving in Scotland - be sure to take a look at the roads on Google street view.

If visiting Liverpool, be sure to visit the nearby historic city of Chester. Between Scotland and Liverpool is the Lake District - which is in my opinion the most scenic area of England.

You don't say how many days you will have for this trip but previous posters have generally been trying to cover too much territory in the time they have available.

Don’t forget that RS has separate forums for Wales & Scotland and I suggest you read some of the back threads in those sections as well as that for England.

Also check out the official Tourist Board websites:>
https://www.visitbritain.com/en
https://www.visitwales.com
https://www.visitscotland.com
https://www.visitengland.com

As for which way round to go it makes little or no difference. There are very fine subtleties to it, but nothing that makes a material difference.
If not coming back to London, but rather to Heathrow Airport, at the end there is a possible case for ending in Wales (going anti clockwise round the circuit). Coming from South Wales you can avoid the transfer through Central London by using the rail/air bus from Reading, and from North Wales the same bus from Watford Junction.- https://www.railair.com/

have you settled on your airfare? If not can you save travel by flying in and out one north and one south airport (multi-city or open jaws)?

Which part of Wales do you intend visiting? North Wales is quite close to Liverpool and has good rail links to coastal towns such as Conwy and Llandudno.
Walk up fares are likely to be expensive. If you can commit to a specificly timed train, you can book and Advance ticket up to 2 weeks before. These will be much cheaper but you have to take the train you have chosen.
I reckon a Two together railcard will be the best for you, £35 but gives 33% discount on off-peak travel.
Be aware that there are airports away from London that have international connections, so no need to go back down to London for the flight home. Manchester and one near Glasgow for example. Manchester has a rail link direct from York to the airport station.

my gosh, thank all of you for your detailed and helpful replies.
a lot to consider.
to answer a few of the questions posted above, our air travel is in & out of London, and we will be approx. 3 weeks in the UK.
loch ness is not an absolute destination, just an example of a potential destination to see in Scotland.
another idea i'm considering is a longer stay in Edinburgh and taking a guided one-day bus tour of other Scottish locations on one of those days. I would like to avoid driving in Scotland if possible.
any recommendations for places to see in Wales are welcomed, but also thinking of just a day trip to Wales (via bus? Train?) from Liverpool.
Again, thank you to all who have offered info. your graciousness is much appreciated.

The bit of Wales between Chester and Colwyn Bay is not that interesting. You would need to reach Conwy / Llandudno to see anything of interest to international travellers. In my opinion, a quick hop into Wales from Liverpool does not do it justice.