Just do it
Nothing you described is needed or beneficial with modern liquid yeast packages. For example Weast's Activator:
The Activator™ package was designed with superior UV light- and oxygen-barrier material to extend shelf life, making our 6 month from manufacture date Product Warranty possible. Yeast slowly depletes energy reserves while in storage. The nutrient pouch inside the Activator™ helps the stored yeast recover from dormancy and restores vitality.
With 6 months guaranteed shelf life, you just need to buy them fresh, and store. That's all. Other manufacturers may not include nutrient pouch, so starter would be advised if they don't, but shelf life can be similar. Dark, airtight container will help.
Make starter after storage period, not before
Fresh commercial liquid yeast packet will have more live cells per ml than your starter. Unless you are experienced microbiologist with good hardware base - but if you were anywhere near that level, you wouldn't need to ask this question. So if you want to spend time making starters, do it just before you brew. Starter before storage may only hurt, starter after storage, or second step to your starter if you already planned it, will help. Much better use of your time.
Tightly capped tubes may be a bad idea
Yeast are alive. They breathe, increasing pressure. Don't know what your tubes are made of, but if they are glass, do not seal them. Not even deoxygenated water one - you don't know how to completely get rid of nutrient manufacturer provided, right?
Your conditions are not sterile
To make a starter, you need a lot of air. If you can afford air filters good enough to give you sterile air in sufficient quantity, you probably don't need to care about splitting packages or anything like that anyway.
To reuse yeast, use slurry from previous brew
Big beers can spend a month or two in fermentation tank. After that, you can collect yeast slurry, and keep it in storage for 2 weeks with no need for starter, and up to 2 months if you know how to wash them and make a starter. This gives you up to 4 months of relatively safe storage, without all these operations, and with high chance of success.
If you only brew twice a year, don't bother
Unless you work way below minimal wage, or minimal wages in your country are even more joke than in mine, your time spent on splitting yeast package probably costs more than a fresh package of yeast. Reusing slurry is only "free" if done relatively fast. So unless it's something extraordinary expensive, or something you expect to be unable to buy again, it's probably best to forget it.