Good post. You've clearly thought this through and asked some pertinent questions.
All rifles are a series of compromises and its up to us to decide which of them are most important.
Milsurp rifles are getting both harder to find and more expensive to acquire and so is the ammunition to feed them. Gone are the days when you could usually find a decent shooter and a few boxes of ammo for three or four hundred bucks. Spare parts availability is also going to be a problem going forward - particularly for some of the less widely distributed guns - and gunsmithing one when you have to fabricate parts is difficult and also prohibitively expensive. Don't get me wrong - I love the old warhorses but I accept them for what they are, warts and all.
The plain fact of the matter today is that it is difficult to find a milsurp rifle that will shoot anywhere near as well as a modern gun. Some will but they are invariably heavier and harder to pack around in the field. Sporterized versions tend to sacrifice accuracy and reliability in the quest for a lighter, handier gun and usually still fall short of the better, post -war, modern designs. A few notable exceptions exist and most are built around Paul Mauser's timeless design or some variant of it.
I can't argue with your choice of the bolt action repeater as a first rifle. They are the single most popular and widespread design world wide for a reason. Today's soldier on the modern battlefield may have need for more than the bolt action battle rifle can deliver but
short of that those rifles can still deliver the goods. As noted above, a Mauser action or some variant of it has been the mainstay of commercially produced hunting rifles for generations and with modern manufacturing techniques they are still about as good a rifle as most of us will ever shoulder.
As new rifles go I can't fault your focus on the Savage and Ruger lines. Very well made for the money. I would also consider Mossberg and Howa in the same general category and roughly the same price range. There's a lot of competition in that class and the decision might well come down to who has your favorite features at the best price. Aftermarket support would be pretty good from any of them so that is probably not a factor. Caliber selection is also pretty good for basic North American hunting rifles. It is still possible to find these rifles gently used for a significant discount from the new, MSRP prices so that might factor in as well.
Used rifles can be great bargains but it requires the buyer to be knowledgeable about a larger universe of guns than just shopping what is new today. It can take some time to acquire that knowledge and also some time to find that one gun that is just right but the payoff is getting a great rifle for a bargain price. Once you expand your potential market to millions of guns produced over decades it requires you to narrow it down to what is best for you in terms of features to look for.
Perhaps it is no surprise that the some of the same manufacturers you look to for possible new guns are the ones you might turn to for a great used on as well. Older Savage and Ruger rifles tend to keep working well year after year given just routine maintenance. The older ( pre Accu-Trigger models ) Savage 110's sometimes look like hell on a stale cracker but often outshoot prettier, more expensive rifles. The same goes for the Savage bargain rifles like the Stevens 200's which were built in the same factory on the same tooling but just given even less attractive stocks. As recently as six months ago I saw examples of both of those rifles that looked to be in very good shape in the $300 - $400 range. A decent scope and maybe a Rifle Basix drop in trigger can have you shooting into an inch at 100 yards with most calibers if you do your part. Handloading can also increase performance and accuracy if you are so inclined.
Rugers will be a little more expensive but are still generally within reach. The older 77 series has proven the equal of "classier" rifles like the Winchesters, Remingtons, Brownings and Weatherbys and, of late, their prices have begun to reflect that. The later Hawkeye series is an improved design that still can be found for reasonable prices used. I never really liked the Ruger integral scope ring mounts but many have used them without complaint - YMMV.
If you decide to stay with the most popular calibers for ammo/reloading component availability going forward I recommend the 7mm's or the American 30's. Any .308 diameter will always have bullets made for it in this country whether it is the .30-30 Winchester, The .30-06 Springfield or the .308 Winchester. Brass is always going to be available somewhere at some price. Powder and primers may get iffy at times but will usually be available somewhere at some price. As for loaded factory ammo - the market for the .30's is just too large to ignore and will be catered to long before other calibers that don't sell as well - even if the gun writers love them.
Everything I just said about the .30's applies to the 7mm's but to a slightly lesser extent. The .270 Winchester is close behind that group and the .243 Winchester is as well. There are just too many rifles out there and too many people shooting them for that market to be completely ignored.
If optics are required you are going to be much better off with a commercial rifle than any milsurp you can name. Period. Milsurp rifles equipped for and with optics are heavy, expensive and generally not suited to schlepping around the game fields for hours or days on end - particularly at altitude.
Learning to get the most out of your old Spanish Mauser sounds like a fun project and a rewarding one until you find another suitable rifle and even then it is always a good idea to have a back up in case the wheels fall off of plan A, eh?