I total my expenses, including reimbursements, non-reimbursed required purchases, and amount spent above reimbursements, and pay myself back fully for them. That stays in the MS account and goes towards future MSing expenses. I just roll that forward. Some months, I put out less than the previous month, but I still pay my self back fully for them. I need at least $2000 on hand, even though I typically only use about $700. Never know which projects will come up.
I never use my own money on shops.
I try to do at least 4 dinner shops a month, and the reimbursement from those are separate from the others. I pay myself back half, and the rest, I use for Me things. New handbag, concert tickets, etc.
My fees go into my kids' college funds. So do reimbursed necessary purchases, like gas station and grocery shops. 10% of my fees are set aside for emergencies.
Some shops, I don't put towards their college fund, or reimburse myself for. For example, I use Cori shops for eBay stock-ups. I find great things on eBay that I'll need, like a $300 winter coat for my husband, I found for $40 on eBay in mid-summer. I paid for it with Cori money.
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Plan the work. Work the plan.