But, I started out long ago. Here is how it rolled.
Started by accident. Foot in the door was someone I knew needed an AS/400 night operator. This job basically entailed loading tapes at given times, and handling print runs and batch jobs, and escalating where needed to 2nd line. That job ran for a while..
That place decided to downsize and change, but the AS/400 stuff gave me enough to go look for more. I ended up in a place with AS/400 and Novell. They moved across adding Win 3.1 and 3.11 and NT4 with MS mail.
This worked through 95 and 95b (at the same time at home at this stage I was running a mob of stuff, a Cyrix IBM 5x68 and some mixed Amiga gear. The office was moving through 286, 386, and 486 gear.
Carried on as AS/400 and PC support continued to cross over, with growing aspect on PCs and support.
Moved to London, carried on, the AS/400 stuff faded and I ended up full on covering PCs, Networks, Servers.
I've been through the whole MS family and I started on Exchange 5 through to the current 2010 release.
Cutting to the chase.
1. Get Technet. I don't know if current circumstances allow MSDN, but get a technet account. Anyone, and I mean anyone working with MS software, PC stuff in their job aspect should have a Technet account. No discussion. No If's, no But's.
2. One of the short comments above was one of the best. Get an MS virtual academy account, and get a trial of Azure.
3. I'll assume you already use virtualisation. If yes, hit 4. If no. Stop everything else. Now go explore Hyper V. Learn it. Learn how to set it up on domain (easier) - and off domain (who made this shit) - and go find a tool called coreconfig from codeplex.
4. Check 3 carefully. Check it again. Anything you are going to build in MS-SQL or with Exchange going forward will likely sit on Hyper V.
5. The requirements of single handedly working on a large scale MS structure of AD, MS-SQL, and Exchange - have basically gotten pretty huge. So large in fact you'll then need to become expert in System Centre. So, slow down. Start to work this carefully. If you plan to do this, and you really mean it, start with some core parts, like Hyper V, and build an exam path and qualify what you can as you go.
6. 5 is an enormous workload today in 2013. If anyone claims otherwise, I think they are talking shit. You are likely to end up majoring in parts, and being laymen in others. My suggestion is that if you choose to do Exchange, and you like it, then built it, test it, exam on it, and make the cert grade. If likewise you work on MS-SQL - and you like it, commit to a focus.
7. The world is full of laymen. Then numbers of people who know enough to be laymen is legion. There are way too few people who really know their shit. In the near future, the laymen are the ones who are heading out of this, don't be one of them.
8. IMHO, although I have said stuff in the above, I believe the above is an environment Microsoft are actively looking to kill, damage, reduce, and replace. As such, be exceptionally aware that you may take the above path and be heading for oblivion. Microsoft are buying more servers than anyone else at this time, and have done this for an extended period of time. Their sole intention to a greater degree is to make cloud their business, and make everyone else out there run their business on the MS cloud. And by MS cloud, I mean a non user serviceable cloud run by Jeffrey Snover level powershelling autobots, because the size and scale by intention is to make what I do now, and what I think you seek to do in near future - too expensive, too slow, and legacy. AD, PC management, Mail, and SQL won't be staying on our Local Lan's, and our users are already mobile. Areas like backup and system management will get automated out, or reduced. So, go look at point 2 carefully. The trial azure account, and learning azure to a level you were considering for Exchange and MS-SQL may be your first step along with Hyper V - and then you may take modifed roads on handling Exchange and MS-SQL azure versions.
9. Learn powershell. I hate it, I think it should be an API people build on, and not the default, but future MS tech's need to be at least reasonably honed on powershell.
10. Put part of your time to one side. Learn Linux, and other technologies, including areas that are within what you call systems. More and more you will face hybrid tech and linux will be part of that.
11. If you run a purist Windows shop, examine DPM. Its an kept quiet, jewel in the crown backup system that MS don't say much about, probably so they don't put noses out of joint with backup players. But test that. Its a seriously good backup option for pure windows operations.
12. Find some people who are peers, on line or similar. Find excellent hang outs, with quality contributors where you can put questions to them and get involved. You will not learn faster than from peers who have seen your problem, and can provide direct solutions. Anyone claiming 'go do this alone' is simply ignoring the volume and challenge involved. You can only progress by levelling up and finding new levels up on a regular basis, and on your own you will plateau too often.
You will find jobs working on your own and off your own back. But you will get better jobs combining experience, a harsh certification program, and job changes as you elevate.
Microsoft lifespan on a product was 11 years for XP, and 3-5 for much of their other range. They are pushing switching to a yearly cycle. *Expect* this to accelerate because yearly cycles will frey existing folks to extinction, and thats frankly by design. MS plans to look after this stuff in due course and is actively making sure you can't. So start thinking about Azure, Virtualisation, and working administration from that side of things.
Side choice. You have some network exams. You could consider the cloud + IP6 on a divergent flightpath, if you have found IP 4 easy to study to cert levels.
Good luck!