Hi PicMas.
For me, information often used or conceptual in nature is usually held available for relatively instant recall. Some bits of seldom used esoteric minutia require that I look them up to be sure! So in the order asked, here goes.
1) Yes. According to the following regulation, a successfully passed practical test for any instructor rating held should re-instate all ratings on the expired certificate. Before beginning a check, verify that the examiner shares this understanding.
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§ 61.199 Expired flight instructor certificates and ratings.
(a) Flight instructor certificates. The holder of an expired flight instructor certificate may exchange that certificate for a new certificate with the same ratings by passing a practical test as prescribed in §61.183(h) of this part for one of the ratings listed on the expired flight instructor certificate.
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2) Probably not, though I cannot quote a rule. I believe it to be the case that only one test at a time may be conducted according to FAA designee policy guidance. However, there is no reason these two tests may not be conducted consecutively in the same day. This can be worked out with the designee you select according to schedule availability.
3) No written is required since you are an ATP seeking only to add a class rating to that certificate.
4) No. Not when practically all research of FARs, AIM, PTS and just about anything else is so easy to do on the web. OK, not exactly easy, but available!
Best regards,
Westhawk